pthread_mutex_init(3) on FreeBSD

The text 0c05c6f413f8, as FreeBSD 3.2-RELEASE, FreeBSD 3.1-RELEASE, FreeBSD 3.0-RELEASE, FreeBSD 2.2.9-RELEASE, FreeBSD 2.2.8-RELEASE shipped it.

create a mutex

pthread_mutex_init(3) on FreeBSD now