2001-07-13  Lutz Mller <urc8@rz.uni-karlsruhe.de>

        * src/sheet-control-gui.[c,h]: Clean up the handling of bonobo objects
        by introducing
        (scg_activate_view_frame) and
        (scg_deactivate_view_frame).
        * src/sheet-object-bonobo.[c,h]: Check for existence of interfaces
        before querying it. Fix ref-counting. Make functions
        (sheet_object_bonobo_load_persist_file),
        (sheet_object_bonobo_load_persist_stream), and
        (sheet_object_bonobo_load_stream) consistent.
        * src/sheet-object-container.c: Parent class is and has ever been
        SheetObjectBonobo. This file should be called
        sheet-object-bonobo-container... Fix ref-counting.
        (cb_user_activation_request): Activate the view frame and set edit mode
        (cb_view_activated): Removed
        (sheet_object_container_new_view): Let the canvas item remember the
        view frame (through gtk_object_set_data)
        * src/sheet-object-container.h: Rename IS_SHEET_CONTAINER_OBJECT to
        IS_SHEET_OBJECT_CONTAINER to be consistent. Remove view_frame
        variable - this object can produce many view frames.