Fix overflow of time.tv_usec in pthreads_synchro_wait_ex() (fix issue #314)

timeval.tv_usec cannot hold values larger than 1000000 thus depending on when pthreads_synchro_wait_ex() is called and the requested timeout the number of microseconds to wait may get larger than 1000000 resulting in an invalid timeout.
Merge pull request #316 from 2072/waitTimeoutFix

Fix overflow of time.tv_usec in pthreads_synchro_wait_ex() (fix issue #3...