Merge pull request #4075 from takluyver/test-pr-pyversions

Update supported Python versions in tools/test_pr
Run python-modernize on our codebase
Fix references to __builtin__ module
Fix local imports in external packages
Run python-modernize on bundled pexpect
Manual fix to bundled pexpect
Update bundled path.py to 4.3
Changes to py3compat
Miscellaneous changes to get IPython running on Python 3.3 without 2to3
Changes to get tests running in Python 3
Various changes to get more tests passing
Fix tab completion tests
Fix nbformat tests
Fix all tests in IPython.core
Fix IPython.config tests
Fix IPython.utils tests
Fix IPython.lib tests
Fix IPython.testing tests
Fix some tests in IPython.kernel
Fix IPython.kernel tests