Also support GPG signature verification of updates, and fix remaining
pylint complaints.
The 2012i release of the tz data reflects the following changes recently
circulated on the tz mailing list:
* Cuba switches from DST [2012-11-04] at 01:00. (Thanks to Steffen Thorsen.)
Change-Id: Ie81d395afa40aa217a0196aad8ca1f9a870bbc31