Issue #12303: run sig*wait*() tests in a subprocesss
Issue #12303: run sig*wait*() tests in a subprocesss

... instead of using fork(): sig*wait*() functions behave differently (not
correctly) after a fork, especially on FreeBSD 6.

Skip also test_sigtimedwait_poll() on FreeBSD 6 because of a kernel bug.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator