Previously, if a review request was uploaded with a parent diff it was

possible that parent diffs would not be attached to FileDiffs in the

case where the parent diff for a file was the result of a rename and a

modify. This would result in the underlying SCM not being able to

locate the parent revision and generate the original file for the

diffviewer.
Now instead of attaching parent diffs to FileDiffs based on the

original file names in the parent diff, we consider the destination

file names. This results in parent diffs being correctly attached when

they contain a renamed and modified file.

Ran unit tests.
Uploaded a review request with a parent diff that had a modified and

renamed file. The diff was visible in the diffviewer when uploaded

with this patch applied; it was not visible when it was uploaded

without the patch applied.