[Web-SIG] WSGI: start_response buffers headers

[Robert Collins]

https://github.com/python-web-sig/wsgi-ng/issues/4

So doing bidirectional streaming is somewhat incompatible with
requiring that headers be buffered until actual server side content is
available (what if the client is meant to write first... but is itself
waiting for the stream to be established).

I think making an empty bytestream flush the headers would be
sufficient, and preserve much of the niceness.

-Rob

-- 
Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud