Add tox and travis config file, update .gitnore.
Install unittest2 as a test dependencies when running tests under Python 2.6.

Currently tests would blow up if they were run under 2.6 because they were
relying on unittest functionality which is only available in Pyton >= 2.7.
Use set instead of set literal, because set literal is only available in Python
> 2.7.
Only run tests which are CPython dependent under CPython.
Also use unittest2 (if available) in tests.integration.init module.
Merge branch 'fix_python_26_test_failures' into enable_integration_tests

Conflicts:
	.travis.yml
	tests/unit/test_marshalling.py
	tox.ini