Sethiddenexit (number)

   Synopsis:
      Toggles a hidden exit

   Notes:
      'Hidden' exits exist in the world, but are not always visible in the room
         description. A hidden exit is always visible in Axmud's automapper
         window.

      This function converts a non-hidden exit into a hidden exit, or vice-
        versa.
      'number' is the number of the exit in the exit model.
      Returns 1 on success, 0 on failure.
