allow command-line edit function to use GUI editor * file-editor-interface.h (file_editor_interface::handle_edit_file_request): New pure virtual function. * file-editor.h, file-editor.cc (file_editor::handle_edit_file_request): New function. * octave-event-listener.h (octave_event_listenter::edit_file): New pure virtual function. * octave-qt-event-listener.h, octave-qt-event-listener.cc (octave_qt_event_listener::edit_file): New function. (octave_qt_event_listener::edit_file_signal): New signal. * main-window.h, main-window.cc (main_window::handle_edit_file_request): New function. (main_window::construct): Connect edit_file_signal to handle_edit_file_request. * __execute_edit_hook__.cc: New file. Provide Fadd_edit_hook, Fremove_edit_hook, and F__execute_edit_hook__ functions for the interpreter. * libinterp/corefcn/module.mk (COREFCN_SRC): Include it in the list. * octave-link.h, octave-link.cc (octave_link::edit_file, octave_link::do_edit_file): New functions. * octave-main-thread.cc (edit_hook_fcn): New function. (octave_main_thread::run): Install it as an edit_hook function. * miscellaneous/edit.m (do_edit): New subfunction. Allow edit request to be intercepted by edit_hook function. (edit): Use it to uniformly handle starting the editor.