Pandas and time zone (tz) info.

[simongarisch]

Hi there.

The current version of pandas throws an error when comparing trading_days (with tz=UTC) to a standard python datetime with no tz info. Basically, it wants the time zone info to be consistent. I've added a few minor changes to make this work.

It also looks like the data coming back for the test file is slightly different. I've modified expected return values slightly, so have a quick look and let me know what you think. The tests should now be passing.

Pandas is also grumbling a touch about Panel => FutureWarning: Panel is deprecated and will be removed in a future version. Perhaps it'd be better to specify a particular pandas version in requirements.txt rather than pandas>=0.17.0... always tough with the Pandas deprecations.

Cheers, Simon.

[Emsu]

@simongarisch happy to merge once tests past. Looks like the test is still failing right now. Thanks for contributing!