This is a workaround for an unsolved travis issue that is causing CI
instances to sporadically fail due to 'unable to connect' issues during
apt stage.

Ref: https://github.com/travis-ci/travis-ci/issues/8507
Ref: https://github.com/travis-ci/travis-ci/issues/9112#issuecomment-376305909

follow-up to a9a7b606

Closes #2428

In order to make curl_multi_timeout() return suitable "sleep" times even
when there's no socket to wait for while the name is being resolved in a
helper thread.

It will increases the timeouts as time passes.

Closes #2419

Closes #2399

- Move the CURL_WERROR option processing after the configuration checks
  to avoid failures in case of warnings during the configuration checks.

This is a partial fix for #2358

This is fixes #2358

If a connection has received a GOAWAY frame while not being used, the
function now reads frames off the connection before trying to reuse it
to avoid reusing connections the server has told us not to use.

Reported-by: Alex Baines
Fixes #1967
Closes #2402

Closes #2414

Reported-by: Michal Trybus

Fixes #2400

Closes #2317

Reported-by: Dongliang Mu
Fixes #2410

Reported-by: Muz Dima

Make the integer overflow check not rely on the undefined behavior that
a size_t wraps around on overflow.

Detected by lgtm.com
Closes #2408

Detected by lgtm.com

Detected by lgtm.com

RFC822 section 5.2 mentions Universal Time, 'UT', to be synonymous with
GMT.

Closes #2401

Currently CMake cannot detect Brotli support. This adds detection of the
libraries and associated header files. It also adds this to the
generated config.

Closes #2392

This patch adds CURLOPT_DNS_SHUFFLE_ADDRESSES to explicitly request
shuffling of IP addresses returned for a hostname when there is more
than one. This is useful when the application knows that a round robin
approach is appropriate and is willing to accept the consequences of
potentially discarding some preference order returned by the system's
implementation.

Closes #1694

To offer applications a more defined behavior, we clear the buffer as
early as possible.

Assisted-by: Jay Satiro

Fixes #2190
Closes #2377

Add --haproxy-protocol for the command line tool

Closes #2162

Reported-by: Vincas Razma
Fixes #2364

When a transfer is requested to get done and it is put in the pending
queue when limited by number of connections, total or per-host, libcurl
would previously very aggressively retry *ALL* pending transfers to get
them transferring. That was very time consuming.

By reducing the aggressiveness in how pending are being retried, we
waste MUCH less time on putting transfers back into pending again.

Some test cases got a factor 30(!) speed improvement with this change.

Reported-by: Cyril B
Fixes #2369
Closes #2383

Especially unpausing a transfer might have to move the socket back to the
"currently used sockets" hash to get monitored. Otherwise it would never get
any more data and get stuck. Easily triggered with pausing using the
multi_socket API.

Reported-by: Philip Prindeville
Bug: https://curl.haxx.se/mail/lib-2018-03/0048.html
Fixes #2393
Closes #2391

 * use member struct event’s instead of pointers to alloc’d struct
   events

 * simplify the cases for the mcode_or_die() function via macros;

 * make multi_timer_cb() actually do what the block comment says it
   should;

 * accept a “stop” command on the FIFO to shut down the service;

 * use cleaner notation for unused variables than the (void) hack;

 * allow following redirections (304’s);

Due to very frequent updates of the rate limit "window", it could
attempt to rate limit within the same milliseconds and that then made
the calculations wrong, leading to it not behaving correctly on very
fast transfers.

This new logic updates the rate limit "window" to be no shorter than the
last three seconds and only updating the timestamps for this when
switching between the states TOOFAST/PERFORM.

Reported-by: 刘佩东
Fixes #2386
Closes #2388

Found via `codespell`

Closes #2389

Closes #2387

Bug: https://github.com/curl/curl/issues/2381

This is what "HTTP/0.9" basically looks like.

Reported on IRC

Closes #2382

It fails somewhere between every 3rd to 10th travis-CI run

Fixes #2380