Issue #8407: Make signal.sigwait() tests more reliable
Issue #8407: Make signal.sigwait() tests more reliable

Block the signal before calling sigwait(). Use os.fork() to ensure that we have
only one thread.

Initial patch written by Charles-François Natali.

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