[MLton] Catching redundant pattern matches

[Jesper Louis Andersen]

Quoting Matthew Fluet (fluet@cs.cornell.edu):

> That is _very_ dangerous to use outside the Basis Library implementation.
> We consider it an undocumented "feature", so if you were led to include it
> in your sources for any reason other than cut-n-paste-ing from the BL
> implementation, please let us know.

Well, I am pretty sure I copied it from inside the BL implementation,
so no alarm.

-- 
jlouis