Thanks, Martin and Demian.  I tweaked the patch slightly before commit, so I've uploaded the diff.  After thinking about it I decided that it does indeed make sense that the new exception subclass both ConnectionResetError and BadStatusLine, exactly because it *isn't* a pure ConnectionError, it is a synthetic one based on getting a '' response when we are expecting a status line.  So I tweaked the language to not mention backward compatibility.  I also tweaked the language of the docs, comments and error message to make it clear that the issue is that the server closed the connection (I understand why you changed it to 'shut down', but I think 'the server closed the connection' is both precise enough and more intuitive).

If you have any issues with the changes I made, let me know.