Work around the PowerPC architecture's +-32KB limitation for conditional
branches by conditionally skipping an unconditional branch instead
(unconditional branches have a +-32MB range).

This requires an extra pass over the basic blocks for each CmmTop after
block sequencing, to determine which branches are "far".

Fixes ticket #709, "Fixup too large" error with -fasm on PowerPC

conc021 is an example of a program that broke.
It doesn't handle them particularly well still, but it doesn't crash at
least.

Also move closeMutex() etc. into freeTaskManager, this is a free-ish thing

 - Added HPCRIX support for passing tracer filename.
 - Added thread tracing support.
 - Cleaned up use of HsFFI.h

Original patch by brianlsmith@gmail.com

This has the undesitrable effect that stg_gc_gen_hp in the RTS was
caught as an HPC symbol and put in the data segment.

This is a minor fix up to the patch
 * retain arity for let-bound vars in simplifier

This time, the PowerPC NCG suffered from a typo.

(I've really grown to hate all those #if foo_TARGET_ARCH
 lines. I need to build GHC for at least four different
 platforms just to make sure that there are no typos...)

We were freeing the tasks in exitScheduler (stopTaskManager) before
exitStorage (stat_exit), but the latter needs to walk down the list
printing stats. Resulted in segfaults with commands like
    ghc -v0 -e main q.hs -H32m -H32m +RTS -Sstderr
(where q.hs is trivial), but very sensitive to exact commandline and
libc version or something.

We now check for freeing memory that isn't allocated, and overwrite memory
we are about to free with 0xaa.
It might be nice to also have a flag to control whether the memory
actually gets free'd.

This patch fixes several bugs in the handling of impliciation
constraints, thereby fixing several regression-suite failures.

On the way I managed to further simplify the code in TcSimplify;
the extra lines are comments.