Rename it to 'httpwant' and make a cloned field in the state struct as
well for run-time updates.
Also: refuse non-supported HTTP versions. Verified with test 129.
Closes#6585
... as we ignore it anyway because servers don't report the correct size
and proftpd even blatantly returns a 550.
Updates a set of tests accordingly.
Reported-by: awesomenode on github
Fixes#6564Closes#6565