Prevent installing Review Board 3.0 on Python 2.6 or lower.
Review Request #355 — Created Jan. 24, 2017 and updated
Review Board 3.0 requires Python 2.7 or higher. This change updates our setup.py to prevent users from accidentally installing it on Python 2.6. Previously, we had checks for different version ranges, recommending different versions of Review Board. We no longer want to recommend anything older than 2.5, as of this release, so those checks and messages have been updated. Testing Done: Tested trying to build with Python 2.6 and 2.7. Reviewed at https://reviews.reviewboard.org/r/8606/