Sorry for the delayed response. Since that pngtest didn't give you any errors, it seems the configure script is drawing some incorrect conclusions about your png library.
(if anyone knows why that would happen, I'd be interested in knowing)
To get the configure script not to shoot itself in the foot anymore, open it in a text editor and find line 5050, which has:
if test -n "$FAILED_PNG"; then
echo "libpng >= 1.0.6 is required for skins."
echo "You can either install the libpng development files,"
echo "or configure with --disable-skins"
Remove that "exit 1
" line, then save the file, and try to configure it again. It will still print the libpng error message, but it won't stop at it. You should then be able to run make and take it from there.
Hope that helps,