pthread_detach(3) on FreeBSD

The text 508a33f8090c, 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.

detach a thread

pthread_detach(3) on FreeBSD now