msgbox.m: use graphics objects to build dialog (bug #42490) * msgbox.m (__msgbox__): New subfunction to build a standard dialog using graphics objects and import standard icons using the GUI's resource_manger. Implement Matlab compatible "opt" argument for changing the "windowstyle" property of the figure and the "interpreter" property of the displayed text. Add BIST for input checks. Update documentation. * errordlg.m, helpdlg.m, warndlg.m: Adapt argument checks. Update documentation. * BaseControl.cc: Prevent BaseControl objects from using invalid pointers to figure objects. * libgui/src/icons/dialog-error.png/svg, dialog-information.png/svg, dialog-warning.png/svg: New fallback Tango icons (png and original svg) for message dialogs. * libgui/src/icons/module.mk: Add new icons to octave_gui_ICONS. * libgui/src/resource.qrc: Add new icons. * libgui/src/icons/icons_license: Add new icons to the list. * octave-link.h (octave_link::message_dialog, octave_link::do_message_dialog): Remove methods. (octave_link::get_named_icon, octave_link::do_get_named_icon): New methods to retrieve an icon pixels by name. * octave-link.cc (F__octave_link_message_dialog__): Remove interpreter function. * octave-link.cc (F__octave_link_named_icon__): New interpreter function. * octave-link.h/cc (octave_qt_link::do_message_dialog) Remove method. (octave_qt_link::do_get_named_icon) Implements octave_link::do_get_named_icon. Make use of resource_manager::icon to get an icon by name and eventually fallback to Tango version.

--- a/libgui/src/module.mk	Sat Oct 06 11:10:36 2018 +0200
+++ b/libgui/src/module.mk	Mon Oct 08 09:16:29 2018 +0200
@@ -9,6 +9,9 @@
   %reldir%/icons/db-step-out.png \
   %reldir%/icons/db-step.png \
   %reldir%/icons/db-stop.png \
+  %reldir%/icons/dialog-error.png \
+  %reldir%/icons/dialog-information.png \
+  %reldir%/icons/dialog-warning.png \
   %reldir%/icons/document-new.png \
   %reldir%/icons/document-open.png \
   %reldir%/icons/document-print.png \