Discover and fix issue #15.

The fix needs to be carried over to casArray as well, and the tests need to be updated.

I'm not sure how this fix should be pushed into GHC... it comes at a bad time re: 7.8.
Apply the fix to casArray as well, currently untested.  Re: #15.
Reenable hello-world target for AtomicPrimops/testing to avoid confusing cabal.  Fix one other minor cabal bug wrt the dependencies.
Another experiment, try __sync_val_compare_and_swap.  This also
fixes issue #15 and passes test n_threads_mutate.  Out of the three
options the GHC version of cas() is the only one that causes the
spurious success errors.
BROKENS STATE.  Try a couple experiments to fix the inline asm for cas().  No luck.
adding ghc 7.8 compatibility to the atomic primops
Fix #15 for real.  The core problem was that ghcplatform.h was not
included and that we were falling back to a sequential version because
WITHSMP was also not defined.
Merge pull request #16 from cartazio/ghc7.8-compat

adding ghc 7.8 compatibility to the atomic primops
Clean out cruft that was put in there while working on #15.  Passes tests on 7.6
Following pull #16, there's really no reason to have the barriers as primops.
We didn't add these primops to GHC 7.8, so for now they're simply C function
calls in both 7.6 and 7.8 and so we can cut out some more cruft.
Bump version for bugfix release
Refactor tests so that all counter variants run the same code.
Add some basic tests revealing issue #18
Add some more basic tests revealing issue #19
Fix issues #18 and #20.
Fill out weak spots in the docs.  Fixes #21.
version bump for bugfix release
Minor update the extra-source-files for tests
minor
minor: rename directory to match package name