Fix WAIT polling interval on POSIX platforms

WAIT with a timeout internally encodes the timeout in milliseconds. The
actual POSIX host implementation however inadvertently uses this value
as a timeout in microseconds. This leads to a de-facto busy loop when
WAITing, as the internal timeouts are simply too short.

Originally discovered by Richard Smolak. Independently reported by
Bohdan Lechnowsky.
Merge pull request #168 from earl/fix-posix-wait-rate

Fix WAIT polling interval on POSIX platforms