Switch Review Board to use Djblets' markdown_escape everywhere

Review Request #7790 — Created Dec. 2, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x

Reviewers

Previously reviewboard.reviews.markdown_utils.markdown_escape became
deprecated. However, several methods in the markdown_utils module
still referred to the old, deprecated markdown_escape. This updates
all usages to use Djblet's version of markdown_escape.

Ran unit tests.