eliminate event listener class * main-window.h, main-window.cc (main_window::exit): New function. (main_window::_ocxtave_qt_event_listener): Delete member variable and all uses. main_window::construct_octave_qt_link): connect _octave_qt_link::octave_thread_finished to main_window::exit. * octave-qt-event-listener.h, octave-qt-event-listener.cc: Delete. * libgui/src/module.mk (octave_gui_MOC, noinst_HEADERS, src_libgui_src_la_SOURCES): Update lists. * octave-qt-link.h, octave-qt-link.cc (octave_qt_link::octave_thread_finished): New signal. (octave_qt_link::~octave_qt_link): Delete main_thread. (octave_qt_link::octave_qt_link): Connect main_thread::finished and main_thread::terminated to octave_qt_link::octave_thread_finished signal. * octave-event-listener.h: Delete. * libinterp/interp-core/module.mk (INTERPFCN_INC): Remove it from the list. * octave-link.h, octave-link.cc (octave_exit_hook): Delete. (octave_link::discard_events, octave_link::do_discard_events, octave_link::exit, octave_link::do_exit): New functions. (octave_link::event_listener): Delete member variable and all uses. (octave_link::about_to_exit, octave_link::register_event_listener, octave_link::do_about_to_exit, octave_link::do_register_event_listener): Delete. (octave_link::accepting_events): New member variable. (octave_link::octave_link): Set octave_exit to octave_link::exit. Initialize accepting_events. (octave_link::do_post_event): Only add to gui_event_queue if accepting_events is true.