Add a DVCS capability gated behind the DVCS feature

Review Request #9905 — Created May 2, 2018 and submitted Aug. 29, 2018, 12:26 p.m. — Latest diff uploaded Aug. 23, 2018, 4:26 p.m.

Information
Owner:	brennie
Repository:	Review Board
Branch:	release-4.0.x
Bugs:
Depends On:	~~9889~~
Blocks:	9920
Commit:	6503100...
Reviewers
Groups:	reviewboard
People:

Description

We now have the review_request.supports_history capability, which is
only present when the dvcs feature is enabled. When disabled, this
capability does not appear in the set of capabilities at all.

Testing Done

Ran unit tests.

You have a pending review.

Review Board 5.0.2 alpha 0 (dev)

Add a DVCS capability gated behind the DVCS feature