prepare for python3 compatibility

We cannot actually implement python3 compat because GitPython does not support python3
as described at https://fedoraproject.org/wiki/User:Churchyard/python3

However, we *can* do a bunch of cleanup and add unit tests to detect regressions.
I originally wrote this changeset as one big patch, but the commit message was ugly,
and `git blame -w` wouldn't really show each of the steps. So I broke it into individual commits.

Feedback?

* resolve build errors on travis-ci
* provide config for editorconfig plugins
* add pep8 tests for syntax errors
* add pep8 tests for deprecated python usage
* add pep8 tests and fix whitespace errors and warnings
* add pep8 tests and fix blank line errors and warnings
* add pep8 tests for import errors
* add pep8 tests and fix statement errors
* add pep8 tests and fix redundant backslashes between brackets
* add pep8 tests and fix lexical indentation for python3
* add unit tests and fix exception clause compatibility
* add unit test and module compatibility lib
* add unit test and use print function for python3 compat
* add python 3.3 to travis-ci build matrix