cmdutil: mark dirstateguard as deprecated

I sincerely doubt this is used in external code, as grepping the
extensions I keep locally (including Facebook's hgexperimental and
evolve) indicate nobody outside of core uses this. As such, I'd also
welcome just dropping this name forward entirely.

mercurial/cmdutil.py

@@ -3522,4 +3522,9 b' def wrongtooltocontinue(repo, task):'
         hint = after[0]
     raise error.Abort(_('no %s in progress') % task, hint=hint)
 
-dirstateguard = dirstateguardmod.dirstateguard
+class dirstateguard(dirstateguardmod.dirstateguard):
+    def __init__(self, repo, name):
+        dirstateguardmod.dirstateguard.__init__(self, repo, name)
+        repo.ui.deprecwarn(
+            'dirstateguard has moved from cmdutil to dirstateguard',
+            '4.1')