support for png 1.5.x, should work fine with 1.4.x - closes #772
support for png 1.5.x, should work fine with 1.4.x - closes #772

git-svn-id: 5adfda8227e14e59fd47d5bd9925a30df16fed74@2961 d397654b-2ff0-0310-9e29-ba003691a0f9

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