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 
On 12/5/2014 17:02, Benjamin Root wrote:
>
> In lib/matplotlib/backends/backend_wx.py:
>
> >              pass
> >
> >          # try to find the set size func across wx versions
> >          try:
> >              getattr(self, 'SetInitialSize')
> >          except AttributeError:
> > -            self.SetInitialSize = getattr(self, 'SetBestFittingSize', do_nothing)
>
> why was this split up? I don't think it exceeded 79 characters.
>
It is 81 characters, I used autopep8 script to get the backend stuff 
PEP8 compliment and it is a bit overzealous in handling long lines.

Werner