There might be situations where a user would want to unset this option.
Avoid forcing him/her to cast the NULL argument to (char *) in order to
get past the compile time typecheck.

Save the errno value immediately after a connect() failure so that it
won't get reset to something else before we read it.

Bug: http://curl.haxx.se/mail/lib-2011-10/0066.html
Reported by: Frank Van Uffelen and Fabian Hiernaux

Jerry Wu detected and provided detailed info about this issue.

When, for a given test, server is instructed to close connection after
server reply we now wait a very small amount of time (50ms) before doing
so. This is done to allow client to, at least partially, read server
reply before getting an ECONNRESET.

The above is required to make test cases 1070, 1200, 1201 and 1202 pass
with Cygwin 1.5.X on W2K.

GOPHER test server closes connection after _every_ server-reply, as such,
at some point it could require a bigger time or using shutdown() before
a server-side initiated disconnection.

both introduced in 42be24af

Set ACK timeout to 5 seconds.

If we are waiting for block X and receive block Y that is the expected one, we
should send ACK and increase X (which is already implemented). Otherwise drop
the packet and don't increase retry counter.

Prevent modification of easy handle being added with curl_multi_add_handle()
unless this function actually suceeds.

Run Curl_posttransfer() to allow restoring of SIGPIPE handler when
Curl_connect() fails early in multi_runsingle().

Move the variable declaration to within the #ifdef

It makes much nicer and less convuluted code everywhere if this struct
member is always present even when libcurl is built without SSL support.

This reverts parts of commit 15e3e451

define away Curl_ntlm_sspi_cleanup() when no windows SSPI build

Modified smtp_endofresp() to detect NTLM from the server specified list
of supported authentication mechanisms.

Modified smtp_authenticate() to start the sending of the NTLM data.

Added smtp_auth_ntlm_type1_message() which creates a NTLM type-1
message. This function is used by authenticate() to start the sending
of data and by smtp_state_auth_ntlm_resp() when the AUTH command
doesn't contain the type-1 message as part of the initial response.
This lack of initial response can happen if an OOM error occurs or the
type-1 message is longer than 504 characters. As the main AUTH command
is limited to 512 character the data has to be transmitted in two
parts; one containing the AUTH NTLM and the second containing the
type-1 message.

Added smtp_state_auth_ntlm_type2msg_resp() which handles the incoming
type-2 message and sends an outgoing type-3 message. This type-2
message is sent by the server in response to our type-1 message.

Modified smtp_state_auth_resp() to handle the response to: the AUTH
NTLM without the initial response and the type-2 response.

Modified smtp_disconnect() to cleanup the NTLM SSPI stack.

Added the output message length as a parameter to both
Curl_ntlm_create_type1_message() and Curl_ntlm_create_type3_message()
for use by future functions that require it.

Updated curl_ntlm.c to cater for the extra parameter on these two
functions.

Changed the name of variable l, in several functions, which represents
the length of strings being sent to the server, to len which is more
meaningful and consistent with other code in smtp.c and elsewhere.

Reworked smtp_authenticate() to be simpler and easier to follow.
Variables and now initialised in their definitions and if no username
and password are specified the function sets the state to SMTP_STOP and
returns immediately, rather than being part of a huge if statement.