Update Mapnik formula to new v2.2.0 release

Merge-able anytime: the release was just tagged, source is available and stable, and release will be announced tomorrow (tuesday): https://github.com/mapnik/mapnik.github.com/pull/5.

Changes also include: 1) removal of `cairomm` and `libtool` dependencies since Mapnik 2.2.0 no longer needs them and 2) removal of a temporary patch that is not longer needed for Mapnik 2.2.0 to compile against boost > 1.52