Edit travisfile with py2.6 addition (and argparse)

argparse will be a requirement for 2.6 support -- switching to optparse will
probably cause problems down the line in a python 3.x variant drops support for
it. Includes fixup to comment in parser to describe py2.6 support
Add python version check to main script

Exits without doing anything if the python version is too old. Does not attempt
to print yet because error printing gets confusing between py2.3 and 3.5. Will
come back to fix this later.
Convert dict comprehension to dict() invocation

Python 2.6 does not support dict comprehensions (and cannot handle them via a
future import.
Convert all multi-clause 'with's to be nested

Python 2.6 does not support multi-clause 'with' statements, so all of these
needed to be converted to nested with statements. Created some trouble with
keeping things within 80 chars for PEP8 compliance.
Merge branch 'feature/py2-6-compat' into dev