test_2_join_in_forked_process fails on FreeBSD 6.4 buildbot.
http://www.python.org/dev/buildbot/all/builders/x86 FreeBSD 6.4 3.x/builds/1606/steps/test/logs/stdio

"""
======================================================================
FAIL: test_2_join_in_forked_process (test.test_threading.ThreadJoinOnShutdown)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_threading.py", line 464, in test_2_join_in_forked_process
    self._run_and_join(script)
  File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_threading.py", line 436, in _run_and_join
    self.assertEqual(data, "end of main\nend of thread\n")
AssertionError: '' != 'end of main\nend of thread\n'
+ end of main
+ end of thread
"""

I think it's the same problem as issue #12316: in the child process, even calling pthread_create can segfault/abort on FreeBSD6 (async-safe blahblah...).
Tests creating a thread from a fork()ed process should be skipped on FreeBSD6.
Patch attached, along with some refactoring to use the skipIf idiom.

As for test_3_join_in_forked_from_thread, well, it could be more or less the same problem. We're really doing something prohibited by POSIX, so things might break in unexpected ways. For example, calling pthread_condition_destroy from the child process can deadlock (see http://bugs.python.org/issue6721#msg136047).

Victor: to debug this kind of problem, it would be great if faulthandler could also dump tracebacks of children processes. Do you mind if I create a new issue?