Add resource to validate DiffCommits

Review Request #7037 — Created March 9, 2015 and submitted — Latest diff uploaded

Information

Review Board
dvcs
94a32f2...

Reviewers

The new ValidateDiffCommitResource is capable of validating the diffs
and metadata of a simple linear history (that is, one where each
commit's diff will apply cleanly to the tracking branch). This new
resource was created because the the commit metadata also has to be
verified and the desired behaviour is different enough from the
existing ValidateDiffResource that it warrants creating a new one
(otherwise the existing ValidateDiffResource would become needlessly
complicated).

Previously, DiffCommits created via the DiffCommitManager's methods
were created even if the save parameter was set to False. This is
now no longer the case.

Fix a flake8 violation in the DiffSetManager.

Ran unit tests.

Able to upload a review request with history and have its commits
validated.