posix-threads.cc (park): Rewrite code to handle time.

2009-11-17  Andrew Haley  <aph@redhat.com>

	* posix-threads.cc (park): Rewrite code to handle time.
	Move mutex lock before the call to compare_and_swap to avoid a
	race condition.
	Add some assertions.
	(unpark): Add an assertion.
	(init): Move here from posix-threads.h.
	* include/posix-threads.h (destroy): removed.

From-SVN: r154265