Patch gtk-jbuhler-980506-0

This patch applies to GTK+ 1.0.1.

I have patched away a few compiler warnings observed compiling GTK with
gcc 2.8.1 -O3 -Wall.  The following three warnings were removed:

* gdk/gdkregion.c: 

Initialized potential uninitialized variable (should be harmless)

* gtk/gtkcontainer.c: 

In two places, the author forgot to cast a GtkAdjustment * to a
GtkObject * when passing it to gtk_object_ref. Should be harmless,
since the caller checks that GTK_IS_ADJUSTMENT (adjustment).

* gtk/gtkselection.c:

In gtk_selection_clear(), selection_info might be used uninitialized.
I initialized it to NULL.  I guess it's safe to assume that if the
caller is passing a selection event, the list of current_selections is
nonempty, but you can't be too careful, especially with that big FIXME
comment in the routine...

Note to GTK developers: *please* compile with -Wall so that this kind
of nit can be squashed before releasing a new GTK version.

                                                 Jeremy Buhler
                                                 jbuhler@cs.washington.edu