adapt to mapnik >= 2.2.0 which does not provide a default ctor for mapnik::projection

git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29289 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
fix compile with clang

git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29290 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
no need to check for mapnik dependencies, just check for mapnik

git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29291 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4