wkhtmltopdf: use more libraries from SlapOS explicitly.

component/wkhtmltopdf/buildout.cfg

 [buildout]
 
 extends = 
+  ../freetype/buildout.cfg
   ../fontconfig/buildout.cfg
-  ../xz-utils/buildout.cfg
+  ../libpng/buildout.cfg
   ../tar/buildout.cfg
   ../xorg/buildout.cfg
+  ../xz-utils/buildout.cfg
+  ../zlib/buildout.cfg
 
 parts =
   wkhtmltopdf
@@ -44,7 +47,7 @@ script =
   wrapper_location = os.path.join("%(location)s", "wkhtmltopdf")
   wrapper = open(wrapper_location, 'w')
   wrapper.write("""#!${dash:location}/bin/dash
-  export LD_LIBRARY_PATH=%(location)s/lib/:${libXrender:location}/lib/:${fontconfig:location}/lib/:${libX11:location}/lib/:${libXext:location}/lib/
+  export LD_LIBRARY_PATH=%(location)s/lib:${fontconfig:location}/lib:${freetype:location}/lib:${libX11:location}/lib:${libXext:location}/lib:${libXrender:location}/lib:${libpng12:location}/lib:${zlib:location}/lib
   export PATH=${fontconfig:location}/bin:$PATH
   exec %(location)s/bin/wkhtmltopdf "$@"
   """)