gdm: create /var/cache/gdm at post install time.

--HG--
branch : gnome3

srcpkgs/gdm/INSTALL

@@ -7,6 +7,7 @@ post)
 		mkdir -p var/log/gdm
 		chown root:gdm var/log/gdm
 	fi
+	[ ! -d var/cache/gdm ] && mkdir -p var/cache/gdm
 	chown gdm:gdm var/lib/gdm > /dev/null
 	chown -R gdm:gdm var/lib/gdm/.gconf.mandatory
 	;;