Summary: Fixes T3679. This comes up every so often and the old script is extremely broad (nuke everything in a repository). Provide a more surgical tool.
Test Plan: Ran a bunch of variations of the script and they all seemed to work OK.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran, staticshock
Maniphest Tasks: T3679
Differential Revision: https://secure.phabricator.com/D6678
