Added a compat module to maintain support of Python 2.6
- This module contains the unittest module, the xml.etree.ElementTree
  module, and the OrderedDict type of Python 2.7, even on Python 2.6.
Modified the PyAirviroException to take format arguments
Cleaned up the unit tests
- Set pyAirviro.tests as test_suite in setuptools.
- Removed nose as a requirement.