Summary:
The old scm-prompt uses this longer, less awesome name.
Let's be backwards compatible with this and all that jazz.
Test Plan: tests pass under bash and zsh
Reviewers: #sourcecontrol, ttung, quark
Reviewed By: quark
Subscribers: quark, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D3597315
Signature: t1:3597315:1469153052:98600400bb3cabf561294fd62f7cc601c280a1bd
