fix conflict between main and editor menus when using alt keys (bug #42659) * file-editor.cc (enable_menu_shortcuts): new function enabling/disabling the alt-key accelerators; (m_add_menu): new function adding a menu and storing menu title with and without the char & indicating the accelerator in a hash; (construct): use m_add_menu for adding a new menu to the menu bar * file-editor-interface.h: new virtual function enable_menu_shortcuts * file-editor.h: new functions enable_menu_shortcuts amd m_add_menu, new hash for storing the menu titles * main-window.cc (connect_visibility_changed): disable editors menu shortcuts; (enable_menu_shortcuts): new function enabling/disabling the alt-key accelerators; (m_add_menu): new function adding a menu and storing menu title with and without the char & indicating the accelerator in a hash; (construct_file_menu, construct_edit_menu, construct_debug_menu, construct_window_menu, construct_help_menu, construct_news_menu): use m_add_menu for adding a new menu to the menu bar; (set_global_edit_shortcuts): enable/disable the main and the editors menu shortcuts

To cite GNU Octave in publications use:

  John W. Eaton, David Bateman, Søren Hauberg, Rik Wehbring (2014).
  GNU Octave version 3.8.1 manual: a high-level interactive language for
  numerical computations.
  CreateSpace Independent Publishing Platform.  ISBN 1441413006,
  URL http://www.gnu.org/software/octave/doc/interpreter/

A BibTeX entry for LaTeX users is:

  @book{,
    author    = {John W. Eaton, David Bateman, S\oren Hauberg, and Rik Wehbring},
    title     = {{GNU Octave} version 3.8.1 manual: a high-level interactive language for numerical computations},
    publisher = {CreateSpace Independent Publishing Platform},
    year      = {2014},
    note      = {{ISBN} 1441413006},
    url       = {http://www.gnu.org/software/octave/doc/interpreter},
  }

We have invested a lot of time and effort in creating GNU Octave, please cite it
when using it.  See also `citation pkgname' for citing Octave packages.