With the changes from bug 143874, GtkSourceView natively uses Pango
fonts for printing and GnomePrint font names are only supported
for backwards compatibility.

This patch switches gedit over to using GtkFontButton and using
Pango font names.

The main complexity in the patch is backwards compatibility with 
the GConf keys - a new set of GConf keys suffixed with _pango
keys are added, and when looking up a font preference, the
algorithm:

 - If the new key is set explicitely, use that
 - If the old key is set explicitely, use that and convert to a 
   Pango font name
 - Otherwise, use the default value for the new key

Setting the key sets the new key only. This system should allow
new and old versions of gedit to be used with the same GConf database.

The files dialogs/gnome-print-font-picker.c
gnome-print-font-dialog.[ch] should be removed when applying this patch.