Add control of track_times to allow reproducible hickling

[ebenolson]

Because h5py includes the creation time by default when creating datasets, saving the same data twice will not produce identical files.

As discussed here, h5py/h5py#225 this is an issue if you want to store files in version control, or do quick comparisons by hashing (in my case, I wanted to verify that my pseudorandom data generator was functioning properly).

[telegraphic]

Hi @ebenolson

Thanks for the pull request. That does sound like useful functionality so I've merged your changes :)

Could you please add a simple test in test_hickle.py to show exactly what this does (and so that we don't accidentally break it in the future)? How do you do your comparisons, with a md5 hash I'm guessing?

[ebenolson]

Thanks, hickle is fantastic but this quirk of HDF5 had me chasing my tail for a while yesterday. Would be nice if it could be set at the file level, but as far as I can tell that's not an option.

I added code to the test file that wraps all the tests and re-runs each twice with track_times disabled, checking that the md5 is equal. It's a bit convoluted because the timestamp granularity is 1 second, and I didn't want to slow it down too much.