Add --break_repo_locks to gclient revert.

CMDupdate and CMDsync have different option parsers, which means they pass 
different options objects to the same underlying code!

R=agable@chromium.org, dnj@chromium.org, smut@chromium.org
BUG=601564

Review URL: https://codereview.chromium.org/1869593004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299777 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -2118,6 +2118,11 @@ def CMDrevert(parser, args):
                     help='don\'t run pre-DEPS hooks', default=False)
   parser.add_option('--upstream', action='store_true',
                     help='Make repo state match upstream branch.')
+  parser.add_option('--break_repo_locks', action='store_true',
+                    help='GIT ONLY - Forcibly remove repo locks (e.g. '
+                      'index.lock). This should only be used if you know for '
+                      'certain that this invocation of gclient is the only '
+                      'thing operating on the git repos (e.g. on a bot).')
   (options, args) = parser.parse_args(args)
   # --force is implied.
   options.force = True