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 16:38, Benjamin Root wrote:
>
> In examples/user_interfaces/embedding_in_wx2.py:
>
> > @@ -4,9 +4,15 @@
> >  toolbar - comment out the setA_toolbar line for no toolbar
> >  """
> >
> > -# Used to guarantee to use at least Wx2.8
> > -import wxversion
> > -wxversion.ensureMinimal('2.8')
> > +import sys
> > +if sys.version_info.major < 3:
> > +    # Used to guarantee to use at least Wx2.8
> > +    import wxversion
> > +    wxversion.ensureMinimal('2.8')
> > +    # wxversion.select('2.8')
> > +    # wxversion.select('2.9.5')
> > +    #wxversion.select('3.0-classic', True)
> > +    #wxversion.select('3.0.2-phoenix', optionsRequired=True)
>
> 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?
>
Phoenix version (only wxPython to run on Py3) does not include 
wxversion, one is supposed to use virtualenv.

I used the above commented lines to be able to test against different 
versions of wxPython.

To clean up they should really all go, the check that we imported at 
least 2.8 is in wx_combat.py.

Will comment the other questions when I have a moment over the weekend 
or early next week.

Werner