Replacement for bin() in python <2.6.

The bin() function was introduced in Python 2.6. Added an existence check for
this built-in and a substitute implementation from
http://code.activestate.com/recipes/219300/#c7.
Test changes for better version compatibility.

- Removed unicode literal tests for Python >3 && <3.3.
- Removed buffer test for Python >3.
- Added +IGNORE_EXCEPTION_DETAIL for PyPy None type tests.
Add Python 3.3 as a TravisCI test target.