use signal for octave_link::edit_file * main-window.h, main-window.cc (main_window::handle_edit_file_request): Delete. (main_window::construct): Delete signal connection from _octave_qt_event_listener::edit_file_signal to main_window::handle_edit_file_request. Connect _octave_qt_link::edit_file_signal to _file_editor::handle_edit_file_request. * qt-event-listener.h, qt-event-listener.cc (octave_qt_event_listener::edit_file): Delete. (octave_qt_event_listener::edit_file_signal): Delete. * octave-qt-link.cc (octave_qt_link::do_edit_file): Emit signal instead of using event listener. * octave-qt-link.h (octave_qt_link::edit_file_signal): New signal. * octave-event-listener.h (octave_event_listener::edit_file): Delete.