handle GTK_RELIEF_HALF, which was introduced to keep either

handle GTK_RELIEF_HALF, which was introduced to keep either

Wed Jul  8 15:31:28 1998  Tim Janik  <timj@gtk.org>

        * gtk/gtkbutton.c: handle GTK_RELIEF_HALF, which was introduced to
        keep either GTK_STATE_NORMAL for relief buttons (GTK_RELIEF_NONE) or
        to still honour GTK_WIDGET_STATE(), e.g. for coloured buttons
        (GTK_RELIEF_HALF).
        (gtk_button_paint): set the background for prelighted buttons with
        GTK_STATE_NORMAL only if GTK_RELIEF_NONE.
        (gtk_button_draw_focus): if GTK_RELIEF_NONE, use GTK_STATE_NORMAL for
        the shadow type (otherwise we get strange shadows for coloured buttons).
        (gtk_button_set_relief): queue a redraw after changing
        the relief.
        (gtk_button_class_init):
        (gtk_button_set_arg):
        (gtk_button_get_arg): added object argument "GtkButton::relief".

        * gtk/gtkenums.h (enum): added GTK_RELIEF_HALF.