Turning @tschaub's FeatureAgent into an event extension.

See http://trac.osgeo.org/openlayers/browser/sandbox/tschaub/select/lib/OpenLayers/FeatureAgent.js. Tests are still missing, but this already works on mobile devices and with Canvas layers. Another possible task would be to make the SelectFeature control use this instead of the Feature handler - then we could get rid of the RootContainer layer for multiple layer selection.