Fixes T12416. See that task for discussion. Slightly older versions of git do not appear to support use of -- to separate flags and arguments.

• Ran bin/repository update PHABX.
• In T12416, had a user with Git 2.1.4 confirm that git ls-remote X worked while git ls-remote -- X failed.
• Read git help ls-remote to look for any kind of suspicious --destroy-the-world flags, didn't see any that made me uneasy.