lstream writing, flushing, & closing

[Ben Wing]

> Do we have any Windows users in the audience who would 
> consent to performing an experiment?  I would like to have 
> somebody run with a modified version of the patch that caused 
> Adrian trouble, but this time call warn_when_safe with data 
> that is about to be discarded from a closing lstream, as well 
> as some information about the lstream itself. Hopefully that 
> will be sufficiently enlightening that we can get rid of that 
> data loss we Linux users have had to suffer from for so long.

I'll do it -- just send me the patch.