We'll be making a small API change to allow SCMTool filename

normalization to make use of the extra_data field. We'll want this to be

3.0.19 and newer, but won't actually remove the deprecation of the older

APIs until 5.0. The release-4.0.x branch has the

RemovedInReviewBoard50Warning and the warn helper method, but 3.0.x

didn't. This change backports it.

Used in conjunction with other changes.