added function to check if a specific signal handler connection exists

added function to check if a specific signal handler connection exists

Thu Feb 24 23:58:44 1999  Tim Janik  <timj@gtk.org>

        * gtk/gtksignal.c (gtk_signal_handler_pending_by_id): added function
        to check if a specific signal handler connection exists (similar to
        gtk_signal_handler_pending_by_func). and yes, this is a neccessary
        addition, since without this function, signal handlers can not be
        (un)blocked or disconnected in a generic fashion without producing
        g_warnings().
        made gtk_signal_get_handlers() an inline function since it's used in
        a lot of places, especially within signal emission.