Fix the Djblets version requirement.

The Djblets version requirement had both a == and <=, which confused
setuptools, leading to the new Djblets not being installed.

This fixes it to be a >=,<= in order to specify a proper range.

With this commit, we're also releasing a hotfixed Review Board 1.7.9.
Update to the latest version of jquery.timesince.

This fixes a problem where errors would be logged when attempting to
operate on elements that were removed. Now, timesince just disconnects
the timer for the removed element.
Merge branch 'release-1.7.x'