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This patch fixes a long standing bug, Trac #179, 
and a recently reported one, Trac #963.

The problem in both cases was an unconstrained type variable 'a', of kind
argTypeKind (printed "??") or openTypeKind ("?").  At top level we now default
the kind of such variables to liftedTypeKind ("*").  This is important because
then instance declarations can match it. The defaulting function is called
TcMType.zonkTopTyVar, and is commented.  (Most of the extra lines in the
patch are comments!)

When doing the fixpoint iteration for 'deriving' we have to be careful
not to end up in a loop, even if we have -fallow-undecidable-instances.

Test is tcfail169

Worker/wrapper generation sometimes has to add a dummy void (State#) argument
to retain laziness.  But when generating the strictness signature for the
worker, I forgot to take account of the extra argument, resulting in a
bogus strictness signature.

Result, chaos.  Trac 317 shows this up, and this patch fixes it.

Fixes stage 2 build with -fvia-C

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. 
				      

In preparation for parallel GC, split up the monolithic GC.c file into
smaller parts.  Also in this patch (and difficult to separate,
unfortunatley):
  
  - Don't include Stable.h in Rts.h, instead just include it where
    necessary.
  
  - consistently use STATIC_INLINE in source files, and INLINE_HEADER
    in header files.  STATIC_INLINE is now turned off when DEBUG is on,
    to make debugging easier.
  
  - The GC no longer takes the get_roots function as an argument.
    We weren't making use of this generalisation.

I don't think this can ever be useful, because to add more roots you
need to do it consistently for every GC.  The right way to add roots
is to use newStablePtr.