Fix ValueError when formatting if continuation lines are incorrectly indented when using autopep8

[lordsutch]

This patch temporarily re-monkey-patches the _checks in pycodestyle to use autopep8's checker, and then patches things back when done. This should fix #771

NB: the patching shouldn't need to be conditional (unlike in pycodestyle_lint.py) since autopep8 always requires pycodestyle to work.

[palantirtech]

Thanks for your interest in palantir/python-language-server, @lordsutch! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[ccordoba12]

Thanks a lot for your contribution! Could you add a test for this?

[lordsutch]

Hmm, I'm not sure why the python 3 test is failing with test/test_language_server.py::test_exit_with_parent_process_died FAILED; that step runs fine on my Mac OS machine.

[ccordoba12]

Thanks @lordsutch!