subrepo: add full revert support for git subrepos

Previously, revert was only possible if the '--no-backup'
switch was specified.
Now, to support backups, we explicitly go over all modified
files in the subrepo.

mercurial/subrepo.py

@@ -1658,10 +1658,14 b' class gitsubrepo(abstractsubrepo):'
     def revert(self, substate, *pats, **opts):
         self.ui.status(_('reverting subrepo %s\n') % substate[0])
         if not opts.get('no_backup'):
-            self.ui.warn('%s: reverting %s subrepos without '
-                         '--no-backup is unsupported\n'
-                         % (substate[0], substate[2]))
-            return []
+            status = self.status(None)
+            names = status.modified
+            for name in names:
+                bakname = "%s.orig" % name
+                self.ui.note(_('saving current version of %s as %s\n') %
+                        (name, bakname))
+                util.rename(os.path.join(self._abspath, name),
+                            os.path.join(self._abspath, bakname))
 
         self.get(substate, overwrite=True)
         return []

tests/test-subrepo-git.t

@@ -787,14 +787,13 b' ensure adding include/exclude ignores th'
 revert the subrepository
   $ hg revert --all
   reverting subrepo ../gitroot (glob)
-  ../gitroot: reverting git subrepos without --no-backup is unsupported (glob)
 
   $ hg status --subrepos
-  M s/foobar
-  A s/barfoo
+  ? s/barfoo
+  ? s/foobar.orig
 
-  $ hg revert --no-backup --all
-  reverting subrepo ../gitroot (glob)
+  $ mv s/foobar.orig s/foobar
+
   $ hg revert --no-backup s
   reverting subrepo ../gitroot (glob)