COMPAT: Support for MPL 1.5
closes https://github.com/pydata/pandas/issues/11111  (nice issue number)

Testing with tox locally I get 1 failure using either matplotlib 1.4 or 1.5. I may have messed up my tox config though. Still need to cleanup a bunch of stuff, I just threw in changes to get each test passing as I went.

release notes et. al coming tonight or tomorrow. Are we making any changes to the build matrix to run a matplotlib 1.5?
