SSLv23_client_method is deprecated starting in OpenSSL 1.1.0. The
equivalent is TLS_client_method.

https://github.com/openssl/openssl/commit/13c9bb3#diff-708d3ae0f2c2973b272b811315381557

Document that if Set-Cookie is used without a domain then the cookie is
sent for any domain and will not be modified.

Bug: http://curl.haxx.se/mail/lib-2015-05/0137.html
Reported-by: Alexander Dyagilev

Previously, after seeing upgrade to HTTP/2, we feed data followed by
upgrade response headers directly to nghttp2_session_mem_recv() in
Curl_http2_switched().  But it turns out that passed buffer, mem, is
part of stream->mem, and callbacks called by
nghttp2_session_mem_recv() will write stream specific data into
stream->mem, overwriting input data.  This will corrupt input, and
most likely frame length error is detected by nghttp2 library.  The
fix is first copy the passed data to HTTP/2 connection buffer,
httpc->inbuf, and call nghttp2_session_mem_recv().

The CURLOPT_COOKIE doc says it "sets the cookie header explicitly in the
outgoing request(s)." However there seems to be some user confusion
about cookie modification. Document that the cookies set by this option
are not modified by the cookie engine.

Bug: http://curl.haxx.se/mail/lib-2015-05/0115.html
Reported-by: Alexander Dyagilev

This function makes a platform-specific absolute path which uses
backslashes on Windows. This form works when passing it on the
command-line, as well as if the source is on another drive.

By (void) prefixing it and adding a comment. Did some minor related
cleanups.

Coverity CID 1299423.

Coverity CID 1299424 identified dead code because of checks that could
never equal true (if the mechanism's name was NULL).

Simplified the function by removing a level of pointers and removing the
loop and array that weren't used.

Replace use of assert with code that properly catches bad input at
run-time even in non-debug builds.

This flaw was sort of detected by Coverity CID 1299425 which claimed the
"case RTSPREQ_NONE" was dead code.

A failed calloc() would lead to NULL pointer use.

Coverity CID 1299427.

non-HTTP proxy implies not using CURLOPT_HTTPPROXYTUNNEL

Bug: http://curl.haxx.se/mail/lib-2015-05/0056.html
Reported-by: Sean Boudreau

Coverity CID 1299428: Dereference after null check (FORWARD_NULL)

Coverity CID 1299426 warned about possible NULL dereference otherwise,
but that would only ever happen if we get invalid HTTP/2 data with
frames for stream 0. Avoid this risk by returning early when stream 0 is
used.

Follow-up fix from b0143a2a

Detected by coverity. CID 1299429

This commit just add implicitly opened stream 1 to streams hash.

Prior to this change the description for SEC_E_ILLEGAL_MESSAGE was OS
and language specific, and invariably translated to something not very
helpful like: "The message received was unexpected or badly formatted."

Bug: https://github.com/bagder/curl/issues/267
Reported-by: Michael Osipov

Refer to b0143a2a for more information on the read-callback change.

This way, the build directory can be located on an entirely different
filesystem from the source code (e.g. a tmpfs).

With many easy handles using the same connection for multiplexing, it is
important we store and keep the transfer-oriented stuff in the
SessionHandle so that callbacks and callback data work fine even when
many easy handles share the same physical connection.

It makes them easier to match output from the nghttpd test server.

Previously, when we send all given buffer in data_source_callback, we
return NGHTTP2_ERR_DEFERRED, and nghttp2 library removes this stream
temporarily for writing.  This itself is good.  If this is the sole
stream in the session, nghttp2_session_want_write() returns zero,
which means that libcurl does not check writeability of the underlying
socket.  This leads to very slow upload, because it seems curl only
upload 16k something per 1 second.  To fix this, if we still have data
to send, call nghttp2_session_resume_data after nghttp2_session_send.
This makes nghttp2_session_want_write() returns nonzero (if connection
window still opens), and as a result, socket writeability is checked,
and upload speed becomes normal.

Stop curl from failing when non-fatal alert is received during
handshake.  This e.g. fixes lots of problems when working with https
sites through proxies.

Reported-by: bsammon
Bug: https://github.com/bagder/curl/issues/282

.. also correct some variable naming in curl_easy_escape.3

Bug: https://github.com/bagder/curl/issues/281


Reported-by:  <bsammon@users.noreply.github.com>

BoringSSL removed support for direct callers of SSL_CTX_callback_ctrl
and SSL_CTX_ctrl, so move to a way that should work on BoringSSL and
OpenSSL.

re #275