BUG/MINOR: mux-h1: verify the request's version before dropping connection: keep...

BUG/MINOR: mux-h1: verify the request's version before dropping connection: keep-alive

The mux h1 properly avoid to set "connection: keep-alive" when the response
is in HTTP/1.1 but it forgot to check the request's version. Thus when the
client requests using HTTP/1.0 and connection: keep-alive (like ab does),
the response is in 1.1 with no keep-alive and ab waits for the close without
checking for the content-length. Response headers actually depend on the
recipient, thus on both request and response's version.

This patch must be backported to 1.9.