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* This is only a slight generalisation of the parser, so that family
  declarations on the toplevel and in classes are uniform.
* I didn't allow that right away as it is a bit tricky to avoid reduce/reduce 
  conflicts.

Haddock documentation comments weren't being treated as comments even
without the -haddock flag.  Fixes nofib/spectral/simple, and probably
others.

This large checkin is the new ghc version of Haskell
Program Coverage, an expression-level coverage tool for Haskell.

Parts:

 - Hpc.[ch] - small runtime support for Hpc; reading/writing *.tix files.
 - Coverage.lhs - Annotates the HsSyn with coverage tickboxes.
  - New Note's in Core,
      - TickBox      -- ticked on entry to sub-expression
      - BinaryTickBox  -- ticked on exit to sub-expression, depending
	       	     -- on the boolean result.

  - New Stg level TickBox (no BinaryTickBoxes, though) 

You can run the coverage tool with -fhpc at compile time. 
Main must be compiled with -fhpc. 
				      

- Not sure whether I do the right thing, because I don't understand the
  doc stuff.  However, the original code was definitely wrong and
  breaking the renaming of family instance declarations.
- The important point is that in

    data instance T pats = rhs

  T is *not* a defining occurence of T (similarly as C is not a defining
  occurence in "instance C Int").

Push this further along, and fix build problems in the first patch.

This large commit combines several interrelated changes:

  - IfaceSyn now contains actual Names rather than the special
    IfaceExtName type.  The binary interface file contains
    a symbol table of Names, where each entry is a (package,
    ModuleName, OccName) triple.  Names in the IfaceSyn point
    to entries in the symbol table.

    This reduces the size of interface files, which should
    hopefully improve performance (not measured yet).

    The toIfaceXXX functions now do not need to pass around
    a function from Name -> IfaceExtName, which makes that
    code simpler.

  - Names now do not point directly to their parents, and the
    nameParent operation has gone away.  It turned out to be hard to
    keep this information consistent in practice, and the parent info
    was only valid in some Names.  Instead we made the following
    changes:

    * ImportAvails contains a new field 
          imp_parent :: NameEnv AvailInfo
      which gives the family info for any Name in scope, and
      is used by the renamer when renaming export lists, amongst
      other things.  This info is thrown away after renaming.

    * The mi_ver_fn field of ModIface now maps to
      (OccName,Version) instead of just Version, where the
      OccName is the parent name.  This mapping is used when
      constructing the usage info for dependent modules.
      There may be entries in mi_ver_fn for things that are not in
      scope, whereas imp_parent only deals with in-scope things.

    * The md_exports field of ModDetails now contains
      [AvailInfo] rather than NameSet.  This gives us
      family info for the exported names of a module.

Also:

   - ifaceDeclSubBinders moved to IfaceSyn (seems like the
     right place for it).

   - heavily refactored renaming of import/export lists.

   - Unfortunately external core is now broken, as it relied on
     IfaceSyn.  It requires some attention.

Linear implicit parameters have been in GHC quite a while,
but we decided they were a mis-feature and scheduled them for
removal.  This patch does the job.

Mon Sep 18 19:42:48 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Option -findexed-types
  Fri Sep  8 21:35:37 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * Option -findexed-types
    - Introduced the switch -findexed-types to activate the indexed type family 
      framework.
    - The switch enables the special 'family' and allows kind signatures (which are
      currently compulsory for associated families).

Mon Sep 18 19:13:47 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Kind sig for toplevel family decls is optional
  Sat Aug 26 19:03:50 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * Kind sig for toplevel family decls is optional
    - Kind sigs are still compulsory for AT family decls.  Changing this is more 
      tricky, as AT decls don't have the family keyword and hence look like empty 
      data decls.  That impacts reduce/reduce conflicts and/or the criteria for 
      checking whether a TyData variant is a family signature.
    - Also removed iso from the syntax (it's still in the lexer in case we want to
      resurrect it). 

Mon Sep 18 18:58:51 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Extend Class.Class to include the TyCons of ATs
  Wed Aug 16 16:15:31 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
    * Extend Class.Class to include the TyCons of ATs

Tue Sep 12 16:57:32 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Type tags in import/export lists
  - To write something like GMapKey(type GMap, empty, lookup, insert)
  - Requires -findexed-types

Tue Aug 15 20:16:00 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Use family and instance keyword to identify indexed types

Tue Aug 15 17:02:53 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Remove checkTopTypeD

Thu Aug  3 19:29:38 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Added error checks & fixed bugs

Tue Aug  1 14:10:39 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Revised kind signatures

Mon Jul 31 17:20:56 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Cleanup (re type function parsing)

Fri Jul 28 21:52:46 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Parser support for assoc synonyms

Wed Jul 26 18:16:25 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Fix migrated AT support
  - Make it compile
  - Successfully parses and renames simple AT declarations
  - Should not affect non-AT programs

Wed Jul 26 17:46:55 EDT 2006  Manuel M T Chakravarty <chak@cse.unsw.edu.au>
  * Migrate cvs diff from fptools-assoc branch
  - Syntactic support for associated types
  - Renamer support for associated types
  - ATs are only allowed with -fglasgow-exts
  - Handle ATs in the type and class declaration kinding knot-tying exercise

Broken up massive patch -=chak
Original log message:  
This is (sadly) all done in one patch to avoid Darcs bugs.
It's not complete work... more FC stuff to come.  A compiler
using just this patch will fail dismally.

I had failed to remove the bit where result type signatures bind
lexical type variables.  And now we are planning to remove them entirely.

This commit therefore does a partial removal (to avoid destablising 6.6).
It also arranges that
	f :: sig = rhs
means a *pattern* binding (not a function binding with no arguments 
and a result signature), which makes sense.

See #815