single threading mlton

[Matthew Fluet]

> > src/mlton/control.sml.  (Maybe it belongs in
> > lib/mlton/basic/proc-env.sml?) 
> 
> Fine with me.  But if I understand your later analysis, the presence
> of engine.sml wasn't actually hurting anything, since Engine.run (and
> hence Signal.handleWith') was never called.

True, but engine.sml is in lib/mlton/basic, so it's considered part of the
user program; hence, not subject to the aggressive dead-code that trims
the basis library.  Since there is reference to Signal.handleWith' in
engine.sml, that pulls in the top level Thread.setHandler and we're toast. 

> correctly.  So, I propose to leave the implementation of
> AppendList.toVector as is, and to replace the implementation of
> Vector.tabulator with the first one I gave above, unless someone can
> think of something even better.

Sounds good to me.