pthread_rwlock_unlock(3) on FreeBSD

The text cb7edef987fd, as FreeBSD 4.4-RELEASE, FreeBSD 4.3-RELEASE, FreeBSD 4.2-RELEASE, FreeBSD 4.1.1-RELEASE, FreeBSD 4.1-RELEASE shipped it.

release a read/write lock

pthread_rwlock_unlock(3) on FreeBSD now