Generate lambdas for uid and gid comparison.

def _Comparator(self, operator):
    """Generate lambdas for uid and gid comparison."""
    if operator == "=":
      return lambda x, y: x == y
    elif operator == ">=":
      return lambda x, y: x >= y
    elif operator == ">":
      return lambda x, y: x > y
    elif operator == "<=":
      return lambda x, y: x <= y
    elif operator == "<":
      return lambda x, y: x < y
    elif operator == "!":
      return lambda x, y: x != y
    raise DefinitionError("Invalid comparison operator %s" % operator)