Equality tests in TrajFile; rename XYZTranslator.

Renamed module and class to match XYZTranslator.

Added equality functions in TrajFile for integration testing:
* `frames_equal(frame1,frame2)`
* `trajs_equal(traj1, traj2)`
Draft of nose tests for XYZTranslator.

More integration tests than unit tests. Current XYZTranslator is far from
passing tests -- there's my goal for the next day! (or two)