Fix invalid argument bug when running in Python3.3

reset_signals() will cause OSError: [Errno 22] Invalid argument when running celery in Python 3.3 on OS X 10.8.3.
It's because signal.getsignal(signal.SIGKILL) and signal.getsignal(signal.SIGSTOP) will return None value.
I've tested the change on my machine, and it fixes the bug.
flakes
Fixes Manager.  Closes #43
Bumps version to 2.7.3.27
Merge branch '2.7'

Conflicts:
	CHANGES.txt
	README.rst
	billiard/__init__.py
	billiard/tests/test_multiprocessing.py
restart_state was not properly resetting time passed.  Fixes celery/celery#1306
Reword ambiguous comment
Adds funtests/ directory
billiard.tests are functional so should be in funtests/
Started unittest suite
signal must reset if SIG_DFL (with tests)
tests for restart_state
Include pid in process info logs
Fixes possible race condition
Bumps version to 2.7.3.28 and updates Changelog
Make sure _exit_function works when thread wakes up after gc collect
Merge branch '2.7'

Conflicts:
	CHANGES.txt
	README.rst
	billiard/__init__.py
	billiard/pool.py
	billiard/util.py