[MLton] Option to show path map

[Stephen Weeks]

> Below is a patch that implements the
> 
>   -show {anns,path-map}
> 
> option and deprecates the
> 
>   -show-anns {false|true}
> 
> option.
> 
> Shall I commit the below patch?

Sure.

> What is the policy for the changelog file?  If I commit the below patch,
> should I also add an entry to the changelog?

Yes.  A changelog entry should be added whenever there is a
user-visible change, and changing a command-line switch certainly
counts.