With Giampaolo's suggested change, all tests pass.  My understanding of 
what asyncore/asynchat is intended to do and how it might be used in 
practice is weak, so I don't feel qualified to comment on the 
correctness of the change.

> One of the issues with using the method that Giampaolo describes, 
which 
> I explained to him, is that generally if someone sends you data, you 
> want to receive it.  You can get both data and the signal that someone 
> disconnected, in particular, with asynchat's .close_when_done() 
method.

Is it possible to add a test for this sort of situation, to make sure 
that future changes take it into account?