Git cherry-pick of commit efac1fce

[BZ #6955]

2008-11-01  Ulrich Drepper  <drepper@redhat.com>
	[BZ #6955]
	* pthread_mutex_lock.c: Add support for private PI mutexes.
	* pthread_mutex_timedlock.c: Likewise.
	* pthread_mutex_trylock.c: Likewise.
	* pthread_mutex_unlock.c: Likewise.
	Patch mostly by Ben Jackson <ben@ben.com>.