Users using the Secure Transport (darwinssl) back-end can now use a
certificate and private key to authenticate with a site using TLS. Because
Apple's security system is based around the keychain and does not have any
non-public function to create a SecIdentityRef data structure from data
loaded outside of the Keychain, the certificate and private key have to be
loaded into the Keychain first (using the certtool command line tool or
the Security framework's C API) before we can find it and use it.

Documented the the option in curl_easy_setopt() and added it to
symbols-in-versions.

...when mentioning login options. Additional minor clarification of
"Windows builds" to be "Windows builds with SSPI"as a way of enabling
NTLM as Windows builds may be built with OpenSSL to enable NTLM or
without NTLM support altogether.

Thanks to archive.org's wayback machine I updated this document with
some facts from the early httpget/urlget web page:

http://web.archive.org/web/19980216125115/http://www.inf.ufrgs.br/~sagula/urlget.html

Relies on CURLOPT_SSL_CTX_FUNCTION, which is OpenSSL specific

Commit c3ea3eb6 introduced some minor cosmetic errors in
curl_mutli_socket_action(3).

Also note the prohibition on sharing handles across threads.

Update sharing interface documentation to provide exhaustive list of
what it does and does not share.

Reported by: Tomas Mlcoch

... so that it adheres to the API documentation.

Reported by: Tomas Mlcoch

Moved SMTP, POP3, IMAP and New Protocol sections to be listed after the
other protocols (FTP, HTTP and TELNET) and SASL to be after SSL and
GnuTLS as these are all security related.

Additionally fixed numbering of the SSL and GnuTLS sections as they
weren't consecutive.

Introducing a number of options to the multi interface that
allows for multiple pipelines to the same host, in order to
optimize the balance between the penalty for opening new
connections and the potential pipelining latency.

Two new options for limiting the number of connections:

CURLMOPT_MAX_HOST_CONNECTIONS - Limits the number of running connections
to the same host. When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished, so we can reuse the connection.

CURLMOPT_MAX_TOTAL_CONNECTIONS - Limits the number of connections in total.
When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished. The free connection will then be reused, if possible, or
closed if the pending handle can't reuse it.

Several new options for pipelining:

CURLMOPT_MAX_PIPELINE_LENGTH - Limits the pipeling length. If a
pipeline is "full" when a connection is to be reused, a new connection
will be opened if the CURLMOPT_MAX_xxx_CONNECTIONS limits allow it.
If not, the handle will be put in a pending state until a connection is
ready (either free or a pipe got shorter).

CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a transfer with a content
length that is larger than this.

CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a chunk larger than this.

CURLMOPT_PIPELINING_SITE_BL - A blacklist of hosts that don't allow
pipelining.

CURLMOPT_PIPELINING_SERVER_BL - A blacklist of server types that don't allow
pipelining.

See the curl_multi_setopt() man page for details.

The flag can be used in pycurl-based applications where using the multi
interface would not be acceptable because of the performance lost caused
by implementing the select() loop in python.

Bug: http://curl.haxx.se/bug/view.cgi?id=1168
Downstream Bug: https://bugzilla.redhat.com/919127