evas: fix building with libpng-1.5
evas: fix building with libpng-1.5

this should work with libpng-1.[245].x; dont know about older versions

git-svn-id: 24a995eca3b83137dd7eab3408044d7832e202f7@57178 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33

antognolli/Evas,antognolli/Evas,antognolli/Evas,antognolli/Evas