[MLton] ref flattening enabled

[Stephen Weeks]

> > One oddity is that the executable compiled with ref flattening is
> > 9,980,206 bytes, while it is only 8,752,477 without ref flattening.
> 
> Any idea as to why this happened?  If anything I would expect the executable to
> shrink.  Is it something that will happen general or is it a specific to this
> particular program?

I believe the problem was operator error.  I must have gotten confused
when running the tests.  I just reran them, and now I see 9,984,830
bytes for the flattened version, and 10,018,798 for the unflattened
version.  That jibes well with the small size improvements from ref
flattening that one typically sees on the benchmarks.  And I still see
a 7% improvement in running time (i.e. self-compile time).