Fix "Need more than 1 value to unpack" with ClearCase.

When generating a clearcase diff by hand and uploading it to an existing review
request, it may not have the desired file revision information in the same
format that RBTools uses. In this case, the filenames won't split correctly.

Testing Done: Actively used.

Fixes bug 3305.

Reviewed at https://reviews.reviewboard.org/r/5713/