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

... introduced in 7f304ab8

The size of the email can now be set via CURLOPT_INFILESIZE. This
allows the email to be rejected by the server, if supported, and the
maximum size has been configured on the server.

Bumped next release version to become 7.23.0 for the changes

Slight rewording of the CURLOPT_URL SMTP sub-section.

Corrected the incorrect use of hyphens on the three uses of
"zero-terminated" with "zero terminated" to match the rest of the
document.

Corrected the use of an out of place hyphen in CURLOPT_NOPROXY section.

It seems some versions of the OpenSSL version defines don't come with L
appended to the number, so let's deal with that nicely.

With locking, plus test, plus documentation

Maximum amount of data a header callback is supposed to get in
a single call from libcurl is limited by the lowest value of
CURL_MAX_WRITE_SIZE and CURL_MAX_HTTP_HEADER.

When using Sun C compiler the preprocessor somehow inserts an extra space
in front of replaced symbol, breaking CURL_CHECK_DEF macro. To workaround
this, macro CURL_CHECK_DEF now ignores all leading whitespace in front of
symbol substitution result.

Removed the code that striped off the domain name when Curl_gethostname
returned the fully qualified domain name as the function has been
updated to return the un-qualified host name.

Replaced the use of HOSTNAME_MAX as the size of the buffer in the call
to Curl_gethostname with sizeof(host) as this is safer should the buffer
size ever be changed.

Moved HOSTNAME_MAX #define into curl_gethostname.h rather than being
locally defined in curl_gethostname.c, curl_ntlm_msgs.c and smtp.c.

Allow (*curl_write_callback) write callbacks to return
CURL_WRITEFUNC_OUT_OF_MEMORY to properly indicate libcurl of OOM conditions
inside the callback itself.

If a socket is larger than FD_SETSIZE, avoid using FD_SET() on the
platforms where this is possible.

Bug: http://curl.haxx.se/bug/view.cgi?id=3413274
Reported by: Tim Starling

When we use binary posts and regular ones intermixed on a single command
line, we cannot do strlen() etc on the data to figure out the length
(when inserting '&' and more). We must therefore keep track of the post
data length. Then we also end up setting the libcurl option with the
known size, so that we don't risk that libcurl will do strlen() on the
data.

This has the minor side-effect that --libcurl source codes now always
will use CURLOPT_POSTFIELDSIZE but I don't consider that terribly
damaging.

Bug: http://curl.haxx.se/bug/view.cgi?id=3413181
Reported by: Taneli Vähäkangas