[6441] new command validatemenus

[Karl Berry]

  ... The new command 
  +    @validatemenus controls whether to check that @menu is given in 
  +    these circumstances.  For Info and HTML output, makeinfo will, when 
  +    needed, create a menu for nodes lacking one given explicitly.

>From the code, isn't the default "on", hence the default behavior is
unchanged?  I hope so.  In which case, the NEWS entry should be clearer
that "@validatemenus off" is needed for the auto-menu-creation.  -k