new function to set the current focus_child of a container, does proper

new function to set the current focus_child of a container, does proper

Sun May  3 16:55:43 1998  Tim Janik  <timj@gtk.org>

        * gtk/gtkcontainer.c (gtk_container_set_focus_child): new function to
                set the current focus_child of a container, does proper referencing and
                        adjusts the vadjustment/hadjustment associated with the focus widget.

                                * gtk/gtkwidget.c (gtk_widget_grab_focus): set the focused child on
                                        containers via gtk_container_set_focus_child.

                                                * gtk/gtknotebook.c: modifications to use gtk_container_set_focus_child
                                                        where appropriate.

                                                                * gtk/gtkcontainer.c (gtk_container_remove): removed unsetting of focus
                                                                        child since not every child removal goes through this function (this
                                                                                showed up after gtk_container_set_focus_child() started to reference the
                                                                                        focus_child of a container).

                                                                                                * gtk/gtkwidget.c (gtk_widget_unparent): moved unsetting the focus_child
                                                                                                        of a container from gtk_container_remove into this place.