Starting with FreeBSD 8.0-RELEASE the system uses new tty layer that no
longer supports old style pseudo ttys *unless* pty(4) kernel module is
loaded. However, pty(4) device is still included in GENERIC kernel on
all releases except 10.0-CURRENT (removed in r233271).

  $ emacs -Q
  M-x term
  <hangs here>

  $ sudo kldload pty
  [try again]

A few ways to solve this:
- use openpty() in -lutil like darwin
- add use posix_openpt() support

http://svn.freebsd.org/changeset/base/233271
https://pub.allbsd.org/FreeBSD-snapshots/ # for testing, seems to be down atm