Fix the semantics of usleep
Fix the semantics of usleep

The semantics of all *sleep calls is that it will not return before the delay
has expired.

	* include/libport/windows.hh (usleep): Never wait a shorter time than
	the one required.

aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport