[MLton] cvs commit: OS.Path.joinDirFile does not check argument

[Stephen Weeks]

> >     a non-empty string a corresponds to valid representation of an arc
> >     only if fromString a returns {isAbs=false, vol="", arcs=[a]}. 
> > 
> > All the implementations agree that fromString "" does indeed return 
> > {isAbs=false, vol="", arcs=[a]}.
> 
> I presume you mean      arcs=[]  ?

Whoops.  Yes.