Replace clock_gettime with gettimeofday.

clock_gettime(CLOCK_REALTIME) is unimplemented on OS X
Increase timing tolerance

Slow and/or busy machines would constantly fail this test with the previous
tolerance.
Merge branch 'bz/fix-timeo'

* bz/fix-timeo:
  Increase timing tolerance
  Replace clock_gettime with gettimeofday.