Unit test attempts to import wrong version of data_io.py

[Who8MyLunch]

While investigating a problem in issue #1, I noticed that the unit test is expecting to import an older version of the data_io.py module. That older version supported reading/writing from a large variety of file types, including the ENVI data types referenced in the unit test. The new version was brought in since the older could not be made open-source. The unit test code and data files need to be updated to work properly on other people's computers.