Sync pytz from requirements.txt

pip 1.4 is imminent, and doesn't install pre-release versions if you
don't ask for them - this includes the date-based version of pytz.

Conflicts:
	requirements.txt

Change-Id: I52fa89005dfedf94a469b3601b3c3d6356eb0174
(cherry picked from commit 5abe67709c61ae705526ee41ef13795216ec1eec)