Diffs between two commit histories are now much more easy to visualize.

Since we have information about how commit histories have changed from

RBTools, we can better determine if commits are modified, unmodified, or

re-ordered. This allows for a much better user experience.
NB: This currently only affects the look and feel of the commit history

diff in change descriptions. The diffviewer will be updated in a future

patch.

Ran unit tests.