made deactivation/deletion of the last superuser disabled

enhance performance
overrided User.save() to check whether the user is the last superuser
added test cases for deactivation/deletion for superuser
updated version release notes
Merge pull request #42 from sh1r0/bug867346

made deactivation/deletion of the last superuser disabled
fix to .travis.yml
add temp exclusion for broken pip packages in mavericks
updating a few packages to try to fix travis build
updated pygments
add markupsafe
updated reqs
updated reqs