def dovc(self, cmd):
        """This accepts the arguments of a command, without the actual
        command itself."""
        env = os.environ.copy()
        env['LC_ALL'] = "C"
        d = utils.getProcessOutputAndValue(self.exe, cmd, env=env,
                                           path=self.treetop)
        d.addCallback(self._didvc, cmd)
        return d