set RECEIVES_DEFAULT on init, and a button press on the widget doesn't

set RECEIVES_DEFAULT on init, and a button press on the widget doesn't

Mon Jan 25 11:05:10 1999  George Lebl  <jirka@5z.com>

        * gtk/gtkbutton.c: set RECEIVES_DEFAULT on init, and a
          button press on the widget doesn't grab default anymore

        * gtk/gtkcheckbutton.c,gtk/gtkoptionmenu.c,gtk/gtkradiobutton.c:
          unset RECEIVES_DEFAULT on init

        * gtk/gtkwidget.[ch]: add a RECEIVES_DEFAULT flag to widget
          flags

        * gtk/gtkwindow.c,gtk/gtkplug.c: on pressing <enter>, activate
          the focused widget if it is a RECEIVES_DEFAULT widget,
          no matter what the current default_widget is

        * gtk/gtkwindow.c: on focus change, migrate the HAS_DEFAULT
          flag to CAN_DEFAULT widgets if they RECEIVE_DEFAULT as well
          or migrate it back to the default_widget if the focus widget
          doesn't "RECEIVE_DEFAULT"