setpgid(2) on FreeBSD

The text 44aa58f2c8b0, as FreeBSD 2.1.7.1-RELEASE, FreeBSD 2.1.7-RELEASE, FreeBSD 2.1.5-RELEASE, FreeBSD 2.0.5-RELEASE shipped it.

set process group

setpgid(2) on FreeBSD now