BUG/WIP: segfault manifesting with dateutil=2.6 w.r.t. replace when timezones are present
closes #14621

This is very close, but a stubborn fall transition issue. any ideas? (note that this does not solve #7825 but should be a simple change after I think)
cc @ischwabacher 
cc @rockg
cc @sinhrks
cc @adamgreenhall
cc @pganssle  

```
(pandas) [Thu Nov 10 09:14:13 ~/pandas]$ nosetests  pandas/tseries/tests/test_offsets.py pandas/tseries/tests/test_timezones.py  -s 
...................S..S...........................................................................................................................................................................F...........................S..............................................................S...S.......................F................................................................................................................................................
======================================================================
FAIL: test_fallback_plural (pandas.tseries.tests.test_offsets.TestDST)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jreback/pandas/pandas/tseries/tests/test_offsets.py", line 4900, in test_fallback_plural
    expected_utc_offset=hrs_post)
  File "/Users/jreback/pandas/pandas/tseries/tests/test_offsets.py", line 4850, in _test_all_offsets
    self._test_offset(offset_name=name, offset_n=n, **kwds)
  File "/Users/jreback/pandas/pandas/tseries/tests/test_offsets.py", line 4856, in _test_offset
    self.assertTrue(get_utc_offset_hours(t) == expected_utc_offset)
AssertionError: False is not true

======================================================================
FAIL: test_ambiguous_flags (pandas.tseries.tests.test_timezones.TestTimeZoneSupportDateutil)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jreback/pandas/pandas/tseries/tests/test_timezones.py", line 524, in test_ambiguous_flags
    freq="H"))
AssertionError: Times[28 chars]00', tz='dateutil//usr/share/zoneinfo/Europe/London', freq='H') != Times[28 chars]00', tz='dateutil//usr/share/zoneinfo/Europe/London', freq='H')

----------------------------------------------------------------------
Ran 458 tests in 5.788s

FAILED (SKIP=5, failures=2)
```