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Split off a FastBool module, to avoid a circular import with Panic

Patch from Bertram Felgenhauer <int-e@gmx.de>

Fixes the build on OpenBSD (trac #2009). Based on a patch from kili.

Readline.initialize spills some escape sequences to stdout for some terminal
types, potentially spoiling  ghc -e  output. So don't initialize readline
unless we're working interactively on a terminal.
Patch from Bertram Felgenhauer <int-e@gmx.de>

The type checker doesn't support lexically scoped type variables 
unless we are using the RelaxedPolyRec option.  Reasons: see
Note [Scoped tyvars] in TcBinds.

So I've changed DynFlags to add this implication, improved the 
documentation, and simplified the code in TcBinds somewhat.
(It's longer but only because of comments!)
 

It controls the number of simplifier phases run during optimisation. These are
numbered from n to 1 (by default, n=2). Phase 0 is always run regardless of
this flag. The flag is ignored with -O0 since (practically) no optimisation is
performed in that case.

The float-out transformation must handle the case where a coercion
variable is free, which in turn mentions type variables in its kind.
Just like a term variable really.

I did a bit of refactoring at the same time.

Test is tc241

MERGE to stable branch

This patch (which is part of the fix for Trac #2018) makes coercion variables
be handled more uniformly.  Generally, they are treated like dictionaries
in the type checker, not like type variables, but in a couple of places we
were treating them like type variables.  Also when zonking we should use
zonkDictBndr not zonkIdBndr.

Somehow we didn't have a separate flag for impredicativity; now we do.

Furthermore, Trac #2019 showed up a missing test for monotypes in data
constructor return types.  And I realised that we were even allowing
things like
	Num (forall a. a) => ...
which we definitely should not.  

This patch insists on monotypes in several places where we were (wrongly)
too liberal before.

Could be merged to 6.8 but no big deal.

This allows the instance of UserOfLocalRegs to be within Haskell98, and IMHO
 makes the code a little cleaner generally.
This is one small (though tedious) step towards making GHC's code more
 portable...

was instance Outputable CmmGraph
type CmmGraph = LGraph Middle Last
now instance (ctx) => Outputable (LGraph m l),
in module with LGraph where it belongs
This also let us reduce the context of DebugNodes to Haskell98,
leaving that class's only extension being multi-parameter.
(also Outputable (LGraph M Last) with M = ExtendWithSpills Middle
was another redundant instance that was then removed)

UserOfLocalRegs (ZLast Last) isn't Haskell98, but it was just as
good an instance to be UserOfLocalRegs a => UserOfLocalRegs (ZLast a)

See Trac #2004, and Note [Flags and equational constraints] in TcPat.