Modified osg/Drawable::draw(..) so that it uses display list COMPILE
rather than COMPILE_AND_EXECUTE to solve performance problems under
NVidia drivers. The old behavior is still available by comments out
a #define.
Fixed the default compilation list src/osgPlugins/Makefile so that it
compiles by defalt png and gif.
and have updated GeoSet to use mutable values for the _numverts etc, allowing
osg::GeoSet::computeNumVerts() to be a const operation. osg::GeoSet::getNumVerts
is now a const once more, so avoiding compilation problems. Also chaned the new
osgconv orientation code to use a Drawable::AttributeFunctor so it can work on
other Drawables other than just GeoSets.