The leading-slash stripping code strikes again. In this case, an initial

revision of a diff was uploaded prior to an upgrade, and a new version was

uploaded subsequent. The result is that the filenames don't match exactly

because one has leading slashes and the other doesn't.
This change normalizes the filenames to always compare them without leading

slashes when figuring out which files match up with which.

Created two diff revisions and changed the FileDiffs in the database so that

the first one had leading slashes and the second didn't. Before this change, I

see two entries in the interdiff for that file. After, it shows the correct

interdiff.
Tested all permutations of leading slash/no leading slash in interdiff

combinations.