Fix issue with _process_files being too strict in its type-checking.

Review Request #10549 — Created May 9, 2019 and submitted — Latest diff uploaded

Information

Review Board
release-4.0.x
cd2fce6...

Reviewers

A recent change went in to ensure that various things were the correct
string type, but the checking for the result of
SCMTool.parse_diff_revision was too strict, allowing only bytes but
not Revision objects. This would cause diff validation errors when
attempting to post newly-added files.

Was able to post a change including a newly-added file.