support version locks
Remove empty line

to trigger a travis-ci build.
Add unittest2 to requirement

so that the unit tests can run in python 2.6.
Use unittest2 if available
add comment, ger rid of unneeded import
resolve merge
Remove unittest2 from requirements.txt

given that it's not used by the travis build script.
Install unittest2 on python2.6
Merge pull request #1 from lyft/GRN-168-optimistic-locking

support version locks