Brokenness caused by libpng update

[Laurent Blume]

Hello,

The recent libpng update to 1.6 has broken building every package
indirectly depending on it: the .pc files referenced the 1.5 version,
which has now disappeared.

I already can't rebuild ImageMagick, because librsvg's .pc complains. I
can't rebuilt librsvg, because gdk_pixbuf's .pc complains.

Note that because of the way those .pc are used in the configure
scripts, the errors happen during building, and look unrelated, eg:

rsvg.h:31:25: fatal error: glib-object.h: No such file or directory

Even though the glib-object.h is present.

That's because the CFLAGS are improperly set, due to configure not
catching the error while setting them:

$ /opt/csw/bin/pkg-config --cflags gdk-pixbuf-2.0
sh: gnome-config: introuvable
Package libpng15 was not found in the pkg-config search path.
Perhaps you should add the directory containing `libpng15.pc'
to the PKG_CONFIG_PATH environment variable
Package 'libpng15', required by 'GdkPixbuf', not found

Riccardo, since you upgraded, can you please list those issues and
contact each maintainer, in order to fix the dependencies in the right
order?

Thanks,

Laurent