Initialization before prompting user for commands.

        Despite the claims in the Cmd documentaion, Cmd.preloop() is not a stub

def preloop(self):
        """Initialization before prompting user for commands.

        Despite the claims in the Cmd documentaion, Cmd.preloop() is not a stub
        """
        Cmd.preloop(self)    # sets up command completion
        self._hist = []    # No history yet
        self._locals = {}    # Initialize execution namespace for user
        self._globals = {}