Changed the support to a little matrix and added brief explanation of
what ALPN and NPN are for.

Add ALPN and NPN support for NSS. This allows cURL to negotiate
HTTP/2.0 connections when built with NSS.

Not comma, which is an inconsistency and a mistake probably inherited
from the examples section of RFC1867.

This bug has been present since the day curl started to support
multipart formposts, back in the 90s.

Reported-by: Rob Davies
Bug: http://curl.haxx.se/bug/view.cgi?id=1333

When using the multi socket interface, libcurl calls the
curl_multi_timer_callback asking to be woken up after
CURL_TIMEOUT_EXPECT_100 milliseconds.

After the timeout has expired, calling curl_multi_socket_action with
CURL_SOCKET_TIMEOUT as sockfd leads libcurl to check expired
timeouts. When handling the 100-continue one, the following check in
Curl_readwrite() fails if exactly CURL_TIMEOUT_EXPECT_100 milliseconds
passed since the timeout has been set!

It seems logical to consider that having waited for exactly
CURL_TIMEOUT_EXPECT_100 ms is enough.

Bug: http://curl.haxx.se/bug/view.cgi?id=1334

Offer TLSv1.0 to 1.2 by default, still fall back to SSLv3
if --tlsv1[.N] was not specified on the command line.

Fix for bug #1303 (030a2b8c) was not complete.
libcurl still pruned DNS entries added manually
after detecting a dead connection. This test
checks such behavior.

Test-case 1515 reproduces bug #1303, where libcurl
would incorrectly prune DNS entries added via
CURLOPT_RESOLVE after the DNS_CACHE_TIMEOUT had
expired.

Leave the valgrind --gen-suppressions option in there, commented, to
make it easier for next update.

The call stack was modified in 2dc7ad23 so the supressions didn't work
anymore.

... caused false detections of the threaded resolver otherwise

A server might respond with a content-encoding header and a response
that was encoded accordingly in HTTP-draft-09/2.0 mode, even if the
client did not send an accept-encoding header earlier. The server might
not send a content-encoding header if the identity encoding was used to
encode the response.

See:
http://tools.ietf.org/html/draft-ietf-httpbis-http2-09#section-9.3

As this is mandated by the http2 spec draft-09

This patch chooses different approach to integrate HTTP2 into HTTP curl
stack. The idea is that we insert HTTP2 layer between HTTP code and
socket(TLS) layer. When HTTP2 is initialized (either in NPN or Upgrade),
we replace the Curl_recv/Curl_send callbacks with HTTP2's, but keep the
original callbacks in http_conn struct. When sending serialized data by
nghttp2, we use original Curl_send callback. Likewise, when reading data
from network, we use original Curl_recv callback. In this way we can
treat both TLS and non-TLS connections.

With this patch, one can transfer contents from https://twitter.com and
from nghttp2 test server in plain HTTP as well.

The code still has rough edges. The notable one is I could not figure
out how to call nghttp2_session_send() when underlying socket is
writable.

Add ALPN support when using GnuTLS >= 3.2.0. This allows
libcurl to negotiate HTTP/2.0 for https connections when
built with GnuTLS.

See:
http://www.gnutls.org/manual/gnutls.html#Application-Layer-Protocol-Negotiation-_0028ALPN_0029
http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg-04

Add ALPN support when using OpenSSL. This will offer ALPN and NPN to the
server, who can respond with either one or none of the two. OpenSSL >=
1.0.2 is required, which means as of today obtaining a snapshot from
ftp://ftp.openssl.org/snapshot/.

See:
http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg-04
https://github.com/openssl/openssl/blob/ba168244a14bbd056e502d7daa04cae4aabe9d0d/ssl/ssl_lib.c#L1787

no previous prototype for function 'memory_tracking_init'