BUG: support TimedeltaIndex serialization in fixed stores (GH9635)
closes https://github.com/pydata/pandas/issues/9635

Small change to fix issue 9635. I'm a beginner contributor, feel free to crush it out.

I updated your comment with "closes" and a link to the issue. Now Github will automatically close that issue when we merge this.
 A couple more things.
1. Could you add a test for this? Something that fails on master (without your patch), and works on your branch
2. Add a release note in `doc/source/whatsnew/v0.16.1` with a sentence describing the bug.

Actually, that whatsnew file may not exist yet. Once we start merging pull requests for .16.1 it will be there.
 @JonasAbernot pretty good!

will need a release note (wait till the end of the week after I push the file up after we release 0.16.0)
 Woups, this time I may need your help. Are all these commits normal ? I tried the 

```
git fetch upstream
git rebase upstream/master
```

from the wiki.  
Should I come back ? And how ?
 [This](https://github.com/pydata/pandas/wiki/Using-Git#fetch-and-then-rebase-interactively-to-squash-reword-fix-otherwise-change-some-commits) is the one you want.

The `--interactive` should open up a window in your editor. [Here's](https://help.github.com/articles/about-git-rebase/) some more info. Basically you'll squash them all down to the first commit. Ping us in [chat](https://gitter.im/pydata/pandas) if you have any trouble.
