allow applications to set their own socket options.

properly if you removed a "live" handle from a multi handle with
curl_multi_remove_handle().

code when doing pure ipv6 EPRT connections.

command on subsequent requests on a re-used connection unless it has to.

files in the root directory.

send the whole request at once, even though the Expect: header was disabled
by the application. An effect of this change is also that small (< 1024
bytes) POSTs are now always sent without Expect: header since we deem it
more costly to bother about that than the risk that we send the data in
vain.

to support older iconv versions.

systems that prototype them slightly differently.

CURLOPT_NOBODY is set true. PREQUOTE is then run roughly at the same place
in the command sequence as it would have run if there would've been a
transfer.

on a persistent connection and allowed the first to use that header, you
could not disable it for the second request.