[rbslack] Fix escaping of review request summaries.
Review Request #6570 — Created Nov. 8, 2014 and submitted — Latest diff uploaded
We were using Django's escape() for review request summaries, which
covers a variety of characters. However, Slack expects that only
>will ever be escaped, and will show any other entities as-is.
This change adds our own escaping logic in order to not leak entities in
Posted a change with a variety of things that Django would escape. All
characters looked fine in the link.