png: add error messages and fix mapping of non-2^n textures
png: add error messages and fix mapping of non-2^n textures

youprofit/lambdanative,attila-lendvai/lambdanative,emacstheviking/lambdanative,youprofit/lambdanative,emacstheviking/lambdanative,emacstheviking/lambdanative,gale320/lambdanative,VincentToups/lambdanative,gale320/lambdanative,attila-lendvai/lambdanative,gale320/lambdanative,attila-lendvai/lambdanative,VincentToups/lambdanative,youprofit/lambdanative,attila-lendvai/lambdanative,gale320/lambdanative,youprofit/lambdanative,VincentToups/lambdanative,attila-lendvai/lambdanative,emacstheviking/lambdanative,emacstheviking/lambdanative,VincentToups/lambdanative,youprofit/lambdanative,VincentToups/lambdanative,gale320/lambdanative