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

It was added in 7.17.0 and is not deprecated

and the traditional source header

This script is the start of a helper tool that scans a source code and
outputs the most recent libcurl version it finds symbols for. Meaning
that if there's no conditions in the code, that's the earliest libcurl
version the scanned code requires.

It is not added to the Makefile.am yet as it is still a bit crude, but
I'm committing it to keep it and allow us to work on it.

This is a meta symbol. OR this value together with a single specific
auth value to force libcurl to probe for un-restricted auth and if not,
only that single auth algorithm is acceptable.

For example you can use CURLAUTH_DIGEST|CURLAUTH_ONLY to make libcurl
first probe for what method to use, but yet only consider Digest to be
acceptable.

Using _only_ CURLAUTH_DIGEST without the CURLAUTH_ONLY field, will make
libcurl explicitly use Digest right away and not do any probing.

I also documented the filtering logic in the symbol-scan.pl function to
clarify why not all CURL_* symbols are included.

I've made the code intended using curl-style now to look more like other
examples.

My previous "fix" was a bit too invasive but is now fixed again.

An example application source code sending SMTP mail with the multi
interface. It is based on the code Alona Rossen provided, which in turn
is based on existing example/test code, and I converted it even more
into a decent example with a fair multi API use, put the info required
to edit at the top and I added some comments.

I've developed a script I call symbol-scan.pl that scans the curl.h and
multi.h header files and compare the symbols it finds in there with the
symbols symbols-in-versions documents and outputs a report on the
differences.  Using this I've dug through the history to fill up
symbols-in-versions with all the symbols my script found mismatches for.

I will commit symbol-scan.pl separatly and think of a way to put it to
use in the build/tests so that we from now on will get this in-sync
check automatically.

It is for FTP, SMTP, POP3, IMAP at least.

The option takes a parameter that should be 1 or 0 to enable or disable
the feature.

URL: http://curl.haxx.se/bug/view.cgi?id=3086428

The invocation of autoconf's AC_PATH_PROG( ) is not quite right for
finding curl-config. This fix corrects the negative case (where
curl-config is not found).

The macro provides a --with-libcurl option that expects a PREFIX to be
specified and not actually a "directory" in which libcurl will be found.
This now spells that out more clearly.

Reported by: Dan Locks
Bug: http://curl.haxx.se/bug/view.cgi?id=3079891

Make it explicit that setting CURLOPT_DIRLISTONLY to 1 will make libcurl
to list the directory.

all multi and hiper examples:

* don't loop curl_multi_perform calls, that was <7.20.0 style, currently
  the exported multi functions will not return CURLM_CALL_MULTI_PERFORM

all hiper examples:
* renamed check_run_count to check_multi_info
* don't  compare current running handle count with previous value, this
  was the wrong way to check for finished requests, simply call
  curl_multi_info_read
* it's also safe to call curl_multi_remove_handle inside the
  curl_multi_info_read loop.

ghiper.c:
* replaced curl_multi_socket (that function is marked as obsolete) calls
  with curl_multi_socket_action calls (as in hiperfifo.c and
  evhiperfifo.c)

ghiper.c and evhiperfifo.c:
* be smart as hiperfifo.c, don't do uncessary curl_multi_* calls in
  new_conn and main

curl_easy_duphandle() was not properly duping the ares channel. The
ares_dup() function was introduced in c-ares 1.6.0 so by starting to use
this function we also raise the bar and require c-ares >= 1.6.0
(released Dec 9, 2008) for such builds.

Reported by: Ning Dong
Bug: http://curl.haxx.se/mail/lib-2010-08/0318.html

We must not assume gcrypt just because of GnuTLS