the ordering for apply longest first includes the indices

[joanise]

To reproduce, add this test case to test_mappings.py:

    def test_rule_ordering_with_indices(self):
        """a{1}b{3} should be shorter than abc"""
        rules = [{"in": "a{1}b{2}", "out": "x{1}x{2}"}, {"in": "abc", "out": "y"}]
        mapping = Mapping(rules=rules, rule_ordering="apply-longest-first")
        transducer = Transducer(mapping)
        self.assertEqual(transducer("abc").output_string, "y")

it will fail, saying:

FAIL: test_rule_ordering_with_indices (__main__.MappingTest)
a{1}b{3} should be shorter than abc
----------------------------------------------------------------------
Traceback (most recent call last):
  File "./test_mappings.py", line 186, in test_rule_ordering_with_indices
    self.assertEqual(transducer("abc").output_string, "y")
AssertionError: 'xxc' != 'y'
- xxc
+ y