Menu add_page() returns page or -1 now.

Changed menu hotkey treatment to *not* separately interpreting hotkey any more.
I think this was a bug, but don't really know any more why i did it before...

men_selected is public now.
  softboard maybe_run_continuous() will be able to check for that
  and only run while on softboard menu page.

Some more debug code in interpret_men_input() to debug and fix a failure on the DUE.