BUG/MEDIUM: mux-h1: Don't add "transfer-encoding" if message-body is forbidden

BUG/MEDIUM: mux-h1: Don't add "transfer-encoding" if message-body is forbidden

When a HTTP/1.1 or above response is emitted to a client, if the flag
H1_MF_XFER_LEN is set whereas H1_MF_CLEN and H1_MF_CHNK are not, the header
"transfer-encoding" is added. It is a way to make HTX chunking consistent with
H2. But we must exclude all cases where the message-body is explicitly forbidden
by the RFC:

 * for all 1XX, 204 and 304 responses
 * for any responses to HEAD requests
 * for 200 responses to CONNECT requests

For these 3 cases, the flag H1_MF_XFER_LEN is set but H1_MF_CLEN and H1_MF_CHNK
not. And the header "transfer-encoding" must not be added.

See issue #27 on github for details about the bug.

This patch must be backported in 1.9.