Add support for Python 3 via six, some rewriting

[pmlandwehr]

This is my attempt to give flo support for py3k. I've largely used six to replace a few calls, and rewritten some arguments to be more pythonic.

In tests, the output produced by run_functional_tests.sh is essentially identical for this new version and the original; only timestamped directories seemed to differ. (I used Fabric3 for the python 3 runs). That said, I should point out that ALL of my versions - including the pip install - returned identical bad checksums at the two instances where checksums are calculated.

[pmlandwehr]

(Looks like the bad checksum issue will cause the CI to fail, so might need to see about verifying that a bad checksum is indeed correct,first.