Catch unexpected errors when validating diffs.

Review Request #7458 — Created June 26, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
9695cdf...

Reviewers

Unexpected errors could cause the diff validation resource to return a
HTTP 500, which is not very useful. We now catch this and return a more
suitable error, and log a traceback.

Generated a fake exception, and saw the error information logged and
returned through the API.

Had a customer test this as well.