backend_wx CVS update

I've just checked in an update to backend_wx.

This has fixes in the fillable shape classes to support the new
fillColor API.

John, I have thought carefully about your suggestion that
NavigationToolbarWx could be exported, and take only a figure in its
constructor, and I've removed the FigureControlWx stuff, and refactored
FigureWx and NavigationToolbarWx so that the toolbar can be used much as
in your GTK example. I think there is a great benefit in making
matplotlib as similar to use as possible with all backends - from both
the user experience perspective and the API.

Therefore, I have also tried to make the behaviour of the mousewheel
more similar to backend_gtk: backend_wx now performs a 'scroll' action
on whichever button the mouse is currently over.

I discovered what I believe to be a wxPython bug in button event
handling: for some reason, the mouseover does not work until at least
one button has been pressed (as for the menu!). I will look into
work-arounds, as this really is not satisfactory.

I have started to put code into place to support saving to bitmaps. This
doesn't work yet (unless you like your bitmaps in black on a black
background), but I thought it better to try to get a working backend_wx
into CVS for the changes you have made. Most of the 'known' bugs are
either fixed, or I have isolated the problem to peculiarities in
wxPython, so I'm focussing on getting some new functionality into place.
Printing first, then I'll look at using double-buffered drawing as
you've suggested.

Any backend_wx users: I'd love any good suggestions on ways around the
couple of wxPython problems I'm having.