Transition from 2to3 setup code to use of six.py as py2/3 compatibility layer

[joernhees]

As a result from discussions in #373 we decided to try using six as a compatibility layer across python versions instead of on setup 2to3 conversion which might not work in certain environments.

[joernhees]

do we still need ez_setup.py in the project dir? it won't work in py3

[joernhees]

can we drop support for py3.2? u'strings' were re-introduced in py3.3 which would allow us not to change 1000 lines of code...
There still are some problematic lines with ur'strings' as py3.3 does not support this anymore due to \u \U escape inconsistencies. I fear we'll run into problems there.

[dbs]

See https://github.com/dbs/rdflib/tree/six_dbs for a number of additional commits on top of the "six" branch, which maintains 100% passing test coverage for Python 2.7 and brings the number of test failures down to 183 on Python 3.3.

Note that I used r'strings' instead of ur'strings' for a few of these commits; seemed to work just fine.

[dbs]

Pushed a bunch more commits onto https://github.com/dbs/rdflib/tree/six_dbs -- many of the unit tests were hidden behind earlier failures, which once those failures were fixed exposed more failures. Fun!

Python 3.3 is currently running at 177 errors / 28 failures, while Python 2.7 is running at 7 errors / 3 failures (looks like a regression slipped into rdflib/term.py). All in all, I believe we're much closer to the goal. What is left looks pretty hairy, though :/

[joernhees]

yupp, once i find a moment i'll continue this and make sure to pull your changes in.
thanks for helping :)

[joernhees]

@dbs i tried pulling in your fixes, but in the end it seems hopeless as there's too many things broken at once. I'm trying a new attempt in #438 where i'll move things away from 2to3 one by one. Hope this helps keeping the status green ;)

[dbs]

+1 - sounds like a good direction to me