Adds a mask that maps to a given proxy.

def bind_proxy(self, name, proxy):
        """Adds a mask that maps to a given proxy."""
        if not len(name) or name[0] != '/' or name[-1] != '/':
            raise ValueError(
                "name must start and end with '/': {0}".format(name))
        self._folder_proxys.insert(0, (name, proxy))