These tests were supposed to be committed as part of r278904 (aka
b789efea) but I didn't 'git add' them.

	* testsuite/30_threads/shared_timed_mutex/try_lock_until/1.cc: New
	test.
	* testsuite/30_threads/shared_timed_mutex/try_lock_until/2.cc: New
	test.