Python 2.6 has no unittest module, use unittest2 instead.  #75
Some differences noted in XML printing.  Some extra requirements.  Closes #75.

A couple of XML printing tests were commented out because of differences
between the ways that 2.6 and 2.6+ versions of ElementTree print XML.

A 2.6 installation will require one to install ordereddict and
unittest2.
Merge branch 'issue75' into devel