matplotlib/matplotlib — pull request #2515 by tacaswell (2013-10-12 04:53:48+00:00)
Title: overloaded `_make_twin_axes` on `LocateableAxesBase` 

so that twinx and will work.

Didn't worry about a proper doc-string because this should be a private function.

Does not have a test.

Not sure if this is the best way to do this, but it works.