As part of a revised patch at #549 olt offered a more robust method to project map bounds in the case of likely proj4 transform failures along edges.
The problem with this patch is speed - in a multithreaded scenario it can reduce r/s by ~ 10. This is not the fault of the patch but rather the proj4 locks for each transform (even if you compile against proj4 trunk and the mapnik mutexes are not used proj4 still locks internally).
So, more thought needs to be given to how to either optionally enable this support by user control or try to offer it as a fallback somehow. Or fix proj4 :)
[springmeyer] code added in r2942, still not default used in renderer however. needs to be exposed as an option. new ticket for that at #770