Decide on the transfer encoding from the Request and the CGI
header. The behaviour depends on the setting
http:chunked_transfer. If never, even explitic requests are
ignored. If on_request, chunked encoding is used if requested
through the CGI header and allowed by the client. If
if_possible, chunked encoding is used whenever the client
allows for it, which is interpreted as the client supporting
HTTP 1.1 or higher.
Chunked encoding is more space efficient and allows the client
to start processing partial results. The drawback is that errors
lead to incomplete pages instead of a nicely formatted complete
page.
