GdkPixbuf and GnomeCanvasPixbuf changes

[Federico Mena Quintero <federico helixcode com>]

Hello, dudes,

I have made some changes to the way gdk-pixbuf is installed.  Now the
GnomeCanvasPixbuf item is compiled in a tiny libgnomecanvaspixbuf
library that is separate from libgdk_pixbuf.  I have also made it so
that the gnome-config script supports a "gnomecanvaspixbuf" argument
to --libs, --includes, and --modversion.

This enables lunat^H^H^H^H^Hbrave hackers who work on gnome-libs-HEAD
to install gdk-pixbuf without symbol clashes.  People who use
gnome-libs-1-0 and want to use the GnomeCanvasPixbuf item will have to
make some small changes in their build processes.

Please report any problems that I may have introduced.

Sorry for the inconvenience,

  Federico