Move forward to wx 2.8 compatibility

Currently Rummage is basing on wx 2.9 version. But current stable branch of wx is 2.8. To ease a packaging for most recent Linux distributions it's better to have 2.8 compatible version. My commit allows to run Rummage under wx 2.8 and should not break somehow 2.9 version. Will happy to see it in upstream)
So under ubuntu installation will probably have only one external depency: python-wxgtk2.8