improve debugging with the GUI * dialog.h, dialog.cc (cd_or_addpath_dialog): New class. (QUIWidgetCreator::signal_debug_cd_or_addpath): New function. (QUIWidgetCreator::create_debug_cd_or_addpath_dialog): New signal. * file-editor-tab.h, file-editor-tab.cc (file_editor_tab::file_in_path): New function. (file_editor_tab::add_breakpoint_callback, file_editor_tab::remove_breakpoint_callback, file_editor_tab::remove_all_breakpoints_callback): Use file_in_path. Don't cd to the directory containing the file. Don't add 1 to the line number. (file_editor_tab::request_add_breakpoint, file_editor_tab::request_remove_breakpoint): Add 1 to the line number. (file_editor_tab::insert_debugger_pointer, file_editor_tab::delete_debugger_pointer, file_editor_tab::do_breakpoint_marker): Subtract 1 from line. (file_editor_tab::bp_info): Also cache full file name. Change all uses. * file-editor.h, file-editor.cc (file_editor::request_open_file, file_editor::handle_delete_debugger_pointer_request): Don't subtract 1 from line numbers. * main-window.h, main-window.cc (main_window::connect_uiwidget_links): Connect uiwidget_creator::create_debug_cd_or_addpath_dialog to main_window::handle_create_debug_cd_or_addpath_dialog. (main_window::handle_create_debug_cd_or_addpath_dialog): New function. * octave-qt-link.h, octave-qt-link.cc (octave_qt_link::do_debug_cd_or_addpath_error): New function. * load-path.h, load-path.cc (load_path::contains_canonical, load_path::do_contains_canonical): New functions. * octave-link.h (octave_link::debug_cd_or_addpath_error, octave_link::do_debug_cd_or_addpath_error): New functions.

--- a/libinterp/interpfcn/octave-link.h
+++ b/libinterp/interpfcn/octave-link.h
@@ -170,6 +170,14 @@
       : std::list<std::string> ();
   }
 
+  static int debug_cd_or_addpath_error (const std::string& file,
+                                        const std::string& dir,
+                                        bool addpath_option)
+  {
+    return enabled ()
+      ? instance->do_debug_cd_or_addpath_error (file, dir, addpath_option) : 0;
+  }
+
   static void change_directory (const std::string& dir)
   {
     if (enabled ())
@@ -341,6 +349,11 @@
                    const std::list<int>& nc,
                    const std::list<std::string>& defaults) = 0;
 
+  virtual int
+  do_debug_cd_or_addpath_error (const std::string& file,
+                                const std::string& dir,
+                                bool addpath_option) = 0;
+
   virtual void do_change_directory (const std::string& dir) = 0;
 
   virtual void