[MLton] Question on profile.fun

[Matthew Fluet]

> The discussion and improvements to  -const 'Exn.keepHistory true'  had me 
> thinking about other improvements to the profiling infra-structure.  

I went ahead and committed the improvements to the profiling flags as 
discussed in this thread.  See  http://mlton.org/commitlog  for a fuller 
description.

If anyone is using profiling extensively, please let me know if the 
default profiling output has changed in any unexpected ways.