added mousewheel navigation support (patch from agonzalezro)
added mousewheel navigation support (patch from agonzalezro)

ptisserand/landslide,adamzap/landslide,ionelmc/python-darkslide,exciteresearch/landslide,n1k0/landslide,kwangkim/landslide,ptisserand/landslide,kwangkim/landslide,kwangkim/landslide,ionelmc/python-darkslide,netantho/epicslide,n1k0/landslide,ptisserand/landslide,adamzap/landslide,exciteresearch/landslide,ionelmc/python-darkslide,exciteresearch/landslide,adamzap/landslide,netantho/epicslide