[MLton] warnUnused and recursive functions

[Vesa Karvonen]

Just a quick note.  I just noticed that warnUnused doesn't seem
to warn about recursive functions.  For example, given

local
   fun foo () = foo () : unit
   val bar = let fun foo () = foo () : unit in foo end
in
end

and -default-ann 'warnUnused true', MLton will only warn about
bar:

Warning: unused.sml 3.8.
  Unused variable: bar.