Proper handling of 'HAVE_SEM_OPEN' config var which returns None if not present on freebsd7+
win32 is _winapi on Py3.  Closes #46
Bumps version to 2.7.3.29
Fixes ImportError in billiard._ext
Bumps verson to 2.7.3.30
Merge branch '2.7'

Conflicts:
	CHANGES.txt
	README.rst
	billiard/__init__.py
	billiard/_ext.py