make wx backends compatible with wxPython-Phoenix

This is based on the comments made to my previous PR for this.

Note that wxPython Phoenix snapshots can now be installed with pip:
pip install -U --pre -f http://wxpython.org/Phoenix/snapshot-builds/ wxPython_Phoenix 
What are the point of these commented out lines? Also, with respect to the if-statement itself, are you saying that the ensureMinimal is only needed for py2.x? There isn't a need for a similar check in py3k?