Basically as documented in http://hackage.haskell.org/trac/ghc/wiki/KindFact,
this patch adds a new kind Constraint such that:

  Show :: * -> Constraint
  (?x::Int) :: Constraint
  (Int ~ a) :: Constraint

And you can write *any* type with kind Constraint to the left of (=>):
even if that type is a type synonym, type variable, indexed type or so on.

The following (somewhat related) changes are also made:
 1. We now box equality evidence. This is required because we want
    to give (Int ~ a) the *lifted* kind Constraint
 2. For similar reasons, implicit parameters can now only be of
    a lifted kind. (?x::Int#) => ty is now ruled out
 3. Implicit parameter constraints are now allowed in superclasses
    and instance contexts (this just falls out as OK with the new
    constraint solver)

Internally the following major changes were made:
 1. There is now no PredTy in the Type data type. Instead
    GHC checks the kind of a type to figure out if it is a predicate
 2. There is now no AClass TyThing: we represent classes as TyThings
    just as a ATyCon (classes had TyCons anyway)
 3. What used to be (~) is now pretty-printed as (~#). The box
    constructor EqBox :: (a ~# b) -> (a ~ b)
 4. The type LCoercion is used internally in the constraint solver
    and type checker to represent coercions with free variables
    of type (a ~ b) rather than (a ~# b)

This special case was introduced in 228c4743 to
'Fix problem with :i for (:)' but the associated Note
doesn't explain why (:) deserves this treatment but not
e.g. Left and Right.

Removing the special case does not break anything
(including :i (:)) so I guess this is no longer necessary.

Conflicts:

	compiler/rename/RnEnv.lhs

Conflicts:

	compiler/simplCore/SetLevels.lhs

(#5441)

1c2f8953 (symptom was broken
biographical profiling, see #5451).

See Note [mkSelectorBinds]

Fixes Trac #5456, which was a buglet arising from

  commit de9b85fa
  Author: Simon Peyton Jones <simonpj@microsoft.com>
  Date:   Fri Sep 2 17:43:53 2011 +0100

    Export a tiny bit more info with AbstractTyCon (fixes #5424)

It only shows up when compiling with -O0!

The problem is documented in the ticket.  The patch
does two things

1. Make exprOkForSpeculation return False for a non-exhaustive case

2. In SetLevels.lvlExpr, look at the *result* scrutinee, not the
   *input* scrutinee, when testing for evaluated-ness

This was making Text.PrettyPrint.HughesPJ give a lint-bug
when the libraries were compiled with -O2.

It's all caused by phantom type synonyms (which are, generally
speaking, a royal pain).  The fix is simple, but a bit brutal.

See Note [Free type variables of the qvar types].

When we compile -O0 we put type constructors in the interface file
without their data constructors -- an AbstractTyCon.  But in a
client module, to give good pattern-match exhaustiveness warnings,
we need to know the difference between a data type and a newtype.
(The latter can be coerced to another type, but a data type can't.)
See Note [Pruning dead case alternatives] in Unify.

Because we weren't conveying this info, we were getting bogus
warnings about inexhaustive patterm matches with GADTs, and
(confusingly) these warnings woudl come and go depending on
whether you were compiling with -O.

This patch makes AbstractTyCon carry a flag indicating whether
the type constructor is "distinct"; two distinct TyCons cannot
be coerced into eachother (except by unsafeCoerce, in which case
all bets are off).

HEADS UP: interface file format changes slightly, so you need
to make clean.

I had second thoughts on the "data family export" question.
Rather than add a wierd special case it seems better to be
simple and consistent.  So this patch

 * Reverts to the simple behaviour:
     module M where { ... }
   exports only what is defined in M, ie NOT any
   imported data families.
   See Note [Exports of data families] in RnNames

* Documents this behaviour in the user manual, and clarifies
  what was there before.

I found that an imported instance was getting printed with <no
location info>.  Fixing this pushed me into a bit more refactoring
than I intended, but it's all small aesthetic stuff, nothing
fundamental.  Caused some error message to change as a result.

I removed pprDefnLoc from the GHC API because it doesn't seem to be
used.  Name.pprNamedefnLoc and pprDefinedAt are probably more useful
anyway.

When constructing export lists, data families pose an awkward problem,
documented in Note [Exports of data families] in RnNames.  Consider

	   module M where
             import X( D )
             data instance D Int = M1 | M2

Here M exports M1 and M2, obviously, but does it export D?  It would
not usually do so, but if we don't then no one can import M selectively
like this:
           import M( D(M1,M2) )

So we compromise and export D too.  But I made two mistakes

a) Didn't check for conflicts between the extra export of X.D
   and any other exports called "D"

b) Did the extra export for imported things too, not just ones defined
   in this module (ie made the compromise apply much more widely than
   necessary)

This made Programatica (a complex project) break in an obscure
way; (b) caused an export conflict, (a) meant that the conflict
was not spotted, which in turn caused later chaos.

Anyway the fix is easy, and is documented in the Note.

thRdrName is used to construct *binders*, and some of them are
Exact RdrNames, so we need to give them a decent source location.

This parameter controls the allowed depth of reasoning in the
type constraint solver.  Perfectly well-behaved programs can
use deep stacks, and 20 is obviously too small.  (Indeed, if
you don't have UndecidableInstances, the constraint solver
is supposed to terminate, so no limit should be needed.)

Responding to Trac #5395 this patch increases the default
to 200.

Allows you to turn off loading/storing the GHCi command history from/to
the ~/.ghc/ghci_history file.

Even if we are recovering from a typecheck error, we should still do
the right thing for the "closed" flag.  Otherwise we get an assert
failure, and potentially different behaviour when the user fixes
the original type error.

maskUninterruptible state instead of ordinary mask, due to a
misinterpretation of the way the TSO_INTERRUPTIBLE flag works.

Remarkably this must have been broken for quite some time.  Indeed we
even had a test that demonstrated the wrong behaviour (conc015a) but
presumably I didn't look hard enough at the output to notice that it
was wrong.

a) Allow multiple AT decls for in a single instance
b) Allow a free type parameter to be instantiated

Example   class C a where
            type T a x :: *

	  data A
          data B
          instance C Int where
            type T Int A = Int
            type T Int B = Bool

There is no reason to prohibit this, and as we move
towards a proper kind system it may even be useful.

I also updated the documentation to cover this change
and the previous one of allowing free type parameters
for associated families.

For the bind_fvs field of FunBind/PatBind, we need to be careful to
keep track of uses of all functions in this module (although not
imported ones).  Moreover in TcBinds.decideGeneralisationPlan we
need to take note of uses of lexically scoped type variables.

These two buglets led to a (useful) assertion failure in TcEnv.

We had the idea that you might be able to define
a default instance for an associated type family, thus:

   class C a where
     type T a :: *
     type T a = a -> a

It's an idea that makes sense, but it was only 10% implemented.
This patch just removes that misleading 10%.

See Note [Associated families and their parent class]

This patch allows

     class C a where
       type T a b :: *
     instance C Int
       type T Int b = b -> b

That is, T has a type index 'b' that is not one of the class
variables.

On the way I did a good deal of refactoring (as usual), especially in
TcInstDcls.tcLocalInstDecl1, which checks for consistent instantiation
of the class instance and the type instance.  Less code, more
expressiveness.  See Note [Checking consistent instantiation]