Teach remote-curl the 'stateless-connect' command which is used to
establish a stateless connection with servers which support protocol
version 2. This allows remote-curl to act as a proxy, allowing the git
client to communicate natively with a remote end, simply using
remote-curl as a pass through to convert requests to http.
Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>