gnome: cleanup and update() to updateSlot()

[Marko Vendelin]

Hi!

the attached patch replaces NULL with 0 in the gnome frontend code and
makes the frontend to compile again by replacing/adding update() with
updateSlot() where appropriate. It seems that DialogBase is changing its
methods quite often which is one more good reason to establish class
hierarchy among gnome frontend classes.

Marko

patch.gnome.29.10.00.gz