Log Message:
update to 0.18.0
This switches to the gnome-2.28 release branch.

pkgsrc changes:
-depend in docbook-xml-4.5 and scrollkeeper-dtd because these are used
 by some gnome pkgs (should fix PR pkg/42233 by Robert Elz)
-prepare to call xsltproc with the -nonet option
 (commented out for now because it makes xsltproc fail even if no network
 accesses are necessary, needs investigation)