reflect the new forward/backward functions added in r2942 in python
reflect the new forward/backward functions added in r2942 in python

git-svn-id: 5adfda8227e14e59fd47d5bd9925a30df16fed74@2943 d397654b-2ff0-0310-9e29-ba003691a0f9

makinacorpus/mapnik2,makinacorpus/mapnik2,makinacorpus/mapnik2,makinacorpus/mapnik2