Make --auto creates actually work in SVN and HG
--auto doesn't work right now on the implicit --create pathway in SVN and HG because we hit these conditions.
Also improve a message.
Test Plan: Ran "arc diff" in unaffiliated working copies in HG and SVN.
Reviewers: svemir, btrahan, vrana, jungejason
Reviewed By: svemir
Differential Revision: https://secure.phabricator.com/D2187