[PATCH] futex: fix errors in nested key ref-counting

[Darren Hart]

The following patch should address the ref counting issue reported by
Mattieu and Louis as well as one with futex_wait_requeue_pi. I have only
been able to test on a single socket dual core i7 system, I'd like to
see some additional testing.

I have another pair of patches which push the ref-counting out of
unqueue_me() and futex_wait_setup(), but they're exhibiting some
unexpected behavior. I didn't want to hold up this fix on those
cleanups.