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.

... introduced in 7f304ab8

This error could be caused by configure scripts being run with -Werror
-Wall, which would lead to libcurl being detected as unusable.

Don't even declare the struct members for disabled features

Introducing the CURLSHE_NOT_BUILT_IN return code for the share interface
when trying to set a sharing option that has been disabled (or not
enabled) in the library.

When the progress function returns to cancel the request, we must mark
the connection to get closed and it must do to the DONE state.

do_init() must be called as early as possible so that state variables
for new connections are reset early. We could otherwise see that the old
values were still there when a connection was to be disconnected very
early and it would make it behave wrongly.

Bug: http://curl.haxx.se/mail/lib-2011-10/0006.html
Reported by: Vladimir Grishchenko

Previously there was wording that made people uncertain of the exact
rules.

Feedback by: Julien Royer and Georg Lippitsch
URL: http://curl.haxx.se/mail/lib-2011-09/0357.html

Reported by: Marcin Adamski
Bug: http://curl.haxx.se/mail/lib-2011-09/0329.html