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 16:46, Benjamin Root wrote:
>
> In examples/user_interfaces/embedding_in_wx3.py:
>
> > @@ -61,6 +67,11 @@ def __init__(self, parent):
> >          sizer.Add(self.toolbar, 0, wx.GROW)
> >          self.SetSizer(sizer)
> >          self.Fit()
> > +        self.Bind(wx.EVT_PAINT, self.OnPaint)
> > +
> > +    def OnPaint(self, event):
> > +        self.canvas.draw()
> > +        event.Skip()
>
> Could you put in a comment explaining "Skip()"?
>
> Also, why is it that we need to bind a paint event anyway? Is there 
> something wrong with the WX backend? Should we use draw_idle()? So 
> many questions here...
>
Sorry, my mistake, that needs to be removed.  It was a bad attempt on 
fixing a display issue.

Werner