ENH: Added support for Tobii ET in Python 2.7

The Tobii interface now automatically uses either the previous Python
2.6 only Tobii Package, or the new (May, 2013) Python 2.7 Tobii package
depending on which version of python is being run.
Merge pull request #322 from isolver/master

ENH: Python 2.7 support for Tobii Eye Tracker.