docs: 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