use signals instead of event queue for entering/leaving debug mode * file-editor-interface.h (file_editor_interface::handle_enter_debug_mode): Rename from file_editor_interface::handle_entered_debug_mode. Change all uses. (file_editor_interface::handle_exit_debug_mode): Rename from file_editor_interface::handle_quit_debug_mode. Change all uses. * file_editor.h, file_editor.cc (file_editor::handle_enter_debug_mode): Rename from file_editor::handle_entered_debug_mode. Change all uses. (file_editor::handle_exit_debug_mode): Rename from file_editor::handle_quit_debug_mode. Change all uses. * main-window.h, main-window.cc (main_window::handle_enter_debugger): Rename from main_window::handle_entered_debug_mode. Change all uses. (main_window::handle_exit_debugger): Rename from main_window::handle_quit_debug_mode. Change all uses. (main_window::construct): Delete signal connection from _octave_qt_event_listener::entered_debug_mode_signal to main_window::handle_entered_debug_mode. Delete signal connection from _octave_qt_event_listener::quit_debug_mode_signal to main_window::handle_quit_debug_mode. Connect _octave_qt_link::enter_debugger_signal signal to main_window::handle_enter_debugger. Connect _octave_qt_link::exit_debugger_signal signal to main_window::handle_exit_debugger. * octave-qt-event-listener.h, octave-qt-event-listener.cc (octave_qt_event_listener::entered_debug_mode, octave_qt_event_listener::quit_debug_mode): Delete. (octave_qt_event_listener::entered_debug_mode_signal, octave_qt_event_listener::quit_debug_mode_signal): Delete signals. * octave-qt-link.h, octave-qt-link.cc (octave_qt_link::do_enter_debugger_event): Emit enter_debugger_signal. (octave_qt_link::do_execute_in_debugger_event): New function. (octave_qt_link::do_exit_debugger_event): Emit exit_debugger_signal. (octave_qt_link::enter_debugger_signal, octave_qt_link::exit_debugger_signal): New signals. * octave-event-listener.h (octave_event_listener::entered_debug_mode, octave_event_listener::quit_debug_mode): Delete. * input.cc (octave_base_reader::octave_gets): Call octave_link::exit_debugger_event if not debugging. (execute_in_debugger_handler): Rename from exit_debugger_handler. Change all uses. Call octave_link::execute_in_debugger_event instead of octave_link::exit_debugger_event. * octave-link.h, octave-link.cc (octave_link::do_generate_events): Don't call debugging mode functions here. (octave_link::enter_debugger_event): Set instance->debugging to true. (octave_link::execute_in_debugger_event): New function. (octave_link::exit_debugger_event): Don't do anything unless instance->debugging is true. Toggle instance->debugging.