new version of MLton

[Henry Cejtin]

Yes,  MLton  uses  a  few extra features in the primitives.  Here is a way to
compile the new MLton using the old one:

Go into lib/mlton/basic/exn.sml of the new one and change the line
    val history = (* fn _ = [] *) MLton.Exn.history
to
    val history = fn _ = [] (* MLton.Exn.history *)
and then compile that using the old MLton, which should work.  Assuming  that
it does, change the line back and then use the MLton you just made to compile
a final MLton.