GtkScrolledWindow inheritance

[Tim Janik <timj gtk org>]

hi all,

with the recent changes to GtkScrolledWindow and the
upcoming removal of its warning about non-scrollable
widgets, i really think it should inherit from GtkBin
now.

this will reduce the code inside the gtkscrolledwindow.c
and provide its ->child member through the GtkBin strcuture.
since the ->child member got only recently added (it was
renamed from ->viewport to ->child) i don't expect much
code to break, in fact a grep on my current gnome
tree does only reveal two such occasions:

./mc/gnome/gscreen.c:#define CLIST_FROM_SW(panel_list) GTK_CLIST (GTK_SCROLLED_WINDOW (panel_list)->child)
./mc/gnome/gwidget.c:   return GTK_SCROLLED_WINDOW (data)->child;

any objections/comments?

---
ciaoTJ