param: add some more validation checks
reintroduce thread pool unit test

It is reproducing a deadlock on POSIX roughly once per 1M runs
asm: 16bpp assembly code for intra_pred_ang16 - all modes
asm: 10bpp code for chroma interpolation filters
threading: use a pthread conditional variable instead of semaphore

This allows more control over the exact behavior, removes the global nature
of the semaphore on some systems, and will allow the addition of a timed wait
to the Event class.  It appears to resolve the deadlocks reproduced in the
pool test on Mac OS X; hopefully on Linux as well.
threading: add a timedWait() method to Event class