size increase

[Matthew Fluet]

> Having some spare cycles, I figured out that the 2Mb size increase in
> the mlton compiler executable occured between March 23 and March 24.
> Haven't combed through the CVS logs to figure out what changed b/w then.

I think with all the runtime changes (probably dealing with Cygwin's
issues with handlers), something let threads creep back into to compiler.
The .ssa for 0324 has Thread_copyCurrent and Thread_switchTo, so that
pretty effectively inhibits constantProp and localRef.