[MLton] Slow commits again, precommit script broken

[Vesa Karvonen]

I'm in a bit of a hurry right now, so I'll just report that I had to
comment out a section from the precommit script, because it caused my
commit to hang forever.  If you've modified the precommit script
recently, please take a look at the script and fix the issue properly
(make sure that it does the job without causing commits to hang).

-Vesa Karvonen