fix and optimize non-default-type mutex behavior

problem 1: mutex type from the attribute was being ignored by
pthread_mutex_init, so recursive/errorchecking mutexes were never
being used at all.

problem 2: ownership of recursive mutexes was not being enforced at
unlock time.

src/thread/pthread_mutex_init.c

@@ -3,7 +3,6 @@
 int pthread_mutex_init(pthread_mutex_t *m, const pthread_mutexattr_t *a)
 {
 	memset(m, 0, sizeof *m);
-	if (a) {
-	}
+	if (a) m->_m_type = *a & 3;
 	return 0;
 }