BUG: support TimedeltaIndex serialization in fixed stores (GH9635)
closes #9635

Hop, revival of PR9662, after some bad git moves.

whats new is now available for 0.16.1 https://github.com/pydata/pandas/commit/5ebf521eac528f5a4b772e4677f70b689b8b1826
 merged via https://github.com/pydata/pandas/commit/a2a5cec32ab63fe18b5840eb8a7712e9bf99c319

thanks!
