getopt usage help to stderr?

[Andy Valencia]

This seems like something which needs to be straightforward, and 
yet I've spent a good amount of time getting nowhere.

How does one get the usage information which getopt embeds in a 
result, and spit it out to stderr?  The internals show some help 
output, hard-coded to stdout.  As any Posix CLI coder knows, 
that's _not_ where you want error/help output to be forced.  I 
tried variations of:

```d
     (GetoptResult rslt)
     defaultGetoptFormatter!File(stderr, progname, rslt.options);
```

with no success.  Is there really not a rslt.helpString() or 
somesuch?

Thanks,
Andy

p.s. Ironically, I could probably have coded a getopt in less 
time than I've spent on std.getopt....