encrypt the control connection and use the data connection "plain".

FTPS

  handle that is part of a multi handle first removes the handle from the
  stack.

- Added CURLOPT_SSL_SESSIONID_CACHE and --no-sessionid to disable SSL
  session-ID re-use on demand since there obviously are broken servers out
  there that misbehave with session-IDs used.

cache within the multi handle.

  while not fixing things very nicely, it does make the SOCKS5 proxy
  connection slightly better as it now acknowledges the timeout for connection
  and it no longer segfaults in the case when SOCKS requires authentication
  and you did not specify username:password.

them.

allow applications to set their own socket options.

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.

control and data connection, as the existing --ftp-ssl option only requests
it.

set a private pointer added to the internal libcurl hash table for the
particular socket passed in to this function.

tool option named --ftp-alternative-to-user. It provides a mean to send a
particular command if the normal USER/PASS approach fails.