It is now possible to generate the original file for a FileDiff whose

source file was created or modified earlier in the series of uploaded

DiffCommits. This allows the diff viewer to show side by side diffs

in these cases. However, the diff viewer will still show more than one 

side by side diff in this case. This will be addressed in a later

patch.
This patch also allows the original and patched file API resources to

return the files in this case.

Ran unit tests.
Was able to view diffs in the diff viewer that depended on FileDiffs

previously uploaded.