This example shows how to send SMTP with TLS

Add a simple SMTP example program, patterned after some of the existing
examples, and the curl application.

This version addresses issues raised by David Woodhouse on comments in
the simplesmtp.c example.

Bug: http://curl.haxx.se/mail/lib-2010-12/0192.html

The SSL_SERVER_VERIFY_LATER bit in the ssl_ctx_new() call allows the
code to verify the peer certificate explicitly after the handshake and
then the "data->set.ssl.verifypeer" option works.

When no explicit version is selected we should try to use whatever is
best for us, and in the axTLS case that means TLSv1.

Removed trailing whitespace
Removed several compiler warnings
Removed odd backslashes at some line endings

The public axTLS header (at least as of 1.2.7) redefines the memory
functions. We #undef those again immediately after the public header to
limit the damage. This should be fixed in axTLS.

In tradition with other options, have this point to the directory prefix
and not the lib directory. Otherwise we can't set the include path
reliably.

Failed HTTPS tests: 301, 306, 311, 312, 313, 560
311, 312 need more detailed error reporting from axTLS.
313 relates to CRL, which hasn't been implemented yet.

Added axTLS to autotool files and glue code to misc other files.
axtls.h maps SSL API functions, but may change.
axtls.c is just a stub file and will definitely change.

The function that checks if pipelining is possible now requires the HTTP
bit to be set so that it doesn't mistakenly tries to do it for other
protocols.

Bug: http://curl.haxx.se/mail/lib-2010-12/0152.html
Reported by: Dmitri Shubin

The generic timeout code must not check easy handles that are already
completed. Going to completed (again) within there risked decreasing the
number of alive handles again and thus it could go negative.

This regression bug was added in 7.21.2 in commit ca10e28f

It was added in 7.17.0 and is not deprecated

Cleanup fix after Kamil's commit 5c7c9a76

ossl_connect_common() now checks whether or not 'struct
connectdata->state' is equal 'ssl_connection_complete' and if so, will
return CURLE_OK with 'done' set to 'TRUE'. This check prevents
ossl_connect_common() from creating a new ssl connection on an existing
ssl session which causes openssl to fail when it tries to parse an
encrypted TLS packet since the cipher data was effectively thrown away
when the new ssl connection was created.

Bug: http://curl.haxx.se/mail/lib-2010-11/0169.html

It helps to prevent a hangup with some FTP servers in case idle session
timeout has exceeded.  But it may be useful also for other protocols
that send any quit message on disconnect.  Currently used by FTP, POP3,
IMAP and SMTP.

When looping in this function and checking for the timeout being
expired, it was not updating the reference time when calculating the
timediff since previous round which made it think each subsequent loop
to have taken longer than it actually did.

I also modified the function to use the generic Curl_timeleft() function
instead of the custom logic.

Bug: http://curl.haxx.se/bug/view.cgi?id=3112579

When send() and recv() fail, we now store the errno value to allow the
app to access it.

Bug: http://curl.haxx.se/bug/view.cgi?id=3128121
Reported by: Yuri