Enable setting attachment thumbnails through the API.

Review Request #3904 — Created Feb. 22, 2013 and submitted — Latest diff uploaded

Information

Review Board
release-1.7.x

Reviewers

Enable setting attachment thumbnails through the API.

The summary is a bit of a lie. This theoretically allows setting attachment
thumbnails through the API, but it's really just plumbing--it's up to individual
mimetype handlers to actually implement it (if they want).
Used this in conjunction with a review UI extension that takes advantage of it.