libpng's header location is not considered in (at least) splash sub-directory.

component/poppler/buildout.cfg

@@ -20,5 +20,5 @@ url = http://poppler.freedesktop.org/poppler-0.17.1.tar.gz
 environment =
   PATH=${pkgconfig:location}/bin:%(PATH)s
   PKG_CONFIG_PATH=${fontconfig:location}/lib/pkgconfig:${freetype:location}/lib/pkgconfig:${curl:location}/lib/pkgconfig:${libpng:location}/lib/pkgconfig
-  CPPFLAGS=-I${libjpeg:location}/include -I${libtiff:location}/include -I${zlib:location}/include
+  CPPFLAGS=-I${libjpeg:location}/include -I${libpng:location}/include -I${libtiff:location}/include -I${zlib:location}/include
   LDFLAGS=-L${libjpeg:location}/lib -Wl,-rpath=${libjpeg:location}/lib -L${libtiff:location}/lib -Wl,-rpath=${libtiff:location}/lib -L${zlib:location}/lib -Wl,-rpath=${zlib:location}/lib