Add the values in <valuelist> to the list of values for <key>. If <key>
        is not in the dictionary, the values in <valuelist> become the values
        for <key>.

        Example:
          omd = omdict([(1,1)])
          omd.addlist(1, [11, 111])
          omd.allitems() == [(1, 1), (1, 11), (1, 111)]
          omd.addlist(2, [2])
          omd.allitems() == [(1, 1), (1, 11), (1, 111), (2, 2)]

        Returns: <self>.

def addlist(self, key, valuelist=[]):
        """
        Add the values in <valuelist> to the list of values for <key>. If <key>
        is not in the dictionary, the values in <valuelist> become the values
        for <key>.

        Example:
          omd = omdict([(1,1)])
          omd.addlist(1, [11, 111])
          omd.allitems() == [(1, 1), (1, 11), (1, 111)]
          omd.addlist(2, [2])
          omd.allitems() == [(1, 1), (1, 11), (1, 111), (2, 2)]

        Returns: <self>.
        """
        for value in valuelist:
            self.add(key, value)
        return self