Previously, if a parent diff contained a moved file without

modifications, it was possible that the associated FileDiff could end

up with incorrect source revisions and would not display correctly.

When a parent diff only contains a move, we no longer apply it because

it will not affect the content and the patch executable will exit

with an error (as it believe there is only garbage in the patch). This

has been fixed and diffs with moves in the parent diff display

correctly.
Unit tests have been added for two cases:

the case where the parent diff has both a modification and rename;

   and
the case where the parent diff has only a rename.

Ran unit tests. The new unit test that covers a parent diff with only

a rename failed without this patch applied.