[MLton] -stop tc -warn-match false bug

[Matthew Fluet]

The following program:

functor F () :>
   sig
      datatype t = T of unit
   end =
   struct
      datatype t = T of unit
   end

structure S = F ()
fun proj x =
   case x of S.T () => ()

gives:

[fluet@localhost test]$ mlton -stop tc -warn-match false -verbose 1 z.sml
MLton MLTONVERSION (built Sat Jan 31 19:12:20 2004 on localhost)
MLton starting
   Type Check SML starting
   Type Check SML raised in 2.79 + 1.50 (35% GC)
MLton raised in 2.79 + 1.50 (35% GC)
T has no conTycon property

I narrowed it down to the use of a constructor in a pattern, when the
constructor is yielded by a pattern.