Set proper old/new revisions on diff results

This happened to work on the commit detail page, but when using a
custom pretty log template to include the diff list on the log page,
it took the old revision from the topmost view, which may have been of
the form oldsha..newsha. This is inappropriate for a single log entry,
which should always contain the diff against just its parent(s).

Fix this by passing down a new revision as well as an old revision in
DiffList and actually using these where necessary.

Issue: 66
Change-Id: Ie87ea857f2be342ead395d71371fb29912aebb26
3 files changed