Some builds of GCC produce output on both stdout and stderr when --help
--verbose is used.  The 2>&1 redirection caused them to be arbitrarily
interleaved with each other because of stream buffering.  Consequently,
grep failed to match the fvisibility= string in the mixed output, even
though the string was present in GCC's standard output.

This led to silently disabling symbol hiding in some builds of curl.

The HTTP/2 tests brought with commit bf05606e were using the internal
name 'http2' for the HTTP/2 server, while in fact that name was already
used for the second instance of the HTTP server. This made tests using
the second instance (like test 2050) fail after a HTTP/2 test had run.

The server is now known as HTTP/2 internally and within the <server>
section in test cases. 1700, 1701 and 1702 were updated accordingly.

Regression introduced in 5f5b6263 (released in 7.48.0)

Reported-by: Fabian Ruff
Fixes #875

Bug: https://github.com/curl/curl/pull/874
Reported-by: Sergei Nikulov

When CURLOPT_POSTFIELDS is set to an empty string libcurl will send a
zero-byte POST. Prior to this change it was documented as sending data
from the read callback.

This also changes the wording of what happens when empty or NULL so that
it's hopefully easier to understand for people whose primary language
isn't English.

Bug: https://github.com/curl/curl/issues/862
Reported-by: Askar Safin

- Remove some erroneous text.

Closes https://github.com/curl/curl/pull/865

- Enable protocol family logic for IPv6 resolves even when support
for synthesized addresses is enabled.

This is a follow up to the parent commit that added support for
synthesized IPv6 addresses from IPv4 on iOS/OS X. The protocol family
logic needed for IPv6 was inadvertently excluded if support for
synthesized addresses was enabled.

Bug: https://github.com/curl/curl/issues/863
Ref: https://github.com/curl/curl/pull/866
Ref: https://github.com/curl/curl/pull/867

Use getaddrinfo() to resolve the IPv4 address literal on iOS/Mac OS X.
If the current network interface doesn’t support IPv4, but supports
IPv6, NAT64, and DNS64.

Closes #866
Fixes #863

1701 and 1702

... and have test 1700 use that to strip out the nghttpx server: headers

It requires that 'nghttpx' is in the PATH, and it will run the tests
using nghttpx as a front-end proxy in front of the standard HTTP/1 test
server. This uses HTTP/2 over plain TCP.

If you like me have nghttpx installed in a custom path, you can run test 1700
like this:

$ PATH=$PATH:$HOME/build-nghttp2/bin/ ./runtests.pl 1700

Calling QueryContextAttributes with SECPKG_ATTR_APPLICATION_PROTOCOL
fails on Windows < 8.1 so we need to disable ALPN on these OS versions.

Inspiration provide by: Daniel Seither

Closes #848
Fixes #840

LoadLibrary was supplanted by Curl_load_library for security
reasons in 6df916d7.

- Change the parser to not require a minor version for HTTP/2.

HTTP/2 connection reuse broke when we changed from HTTP/2.0 to HTTP/2
in 8243a958 because the parser still expected a minor version.

Bug: https://github.com/curl/curl/issues/855
Reported-by: Andrew Robbins, Frank Gevaerts

connect.c:952:5: warning: suggest explicit braces to avoid ambiguous 'else'

Closes #845

... causing SIGSEGV while parsing URL with too many globs.
Minimal example:

$ curl $(for i in $(seq 101); do printf '{a}'; done)

Reported-by: Romain Coltel
Bug: https://bugzilla.redhat.com/1340757

Closes #850

Dependency added by 6cabd785

Closes #849

Sessionid cache management is inseparable from managing individual
session lifetimes. E.g. for reference-counted sessions (like those in
SChannel and OpenSSL engines) every session addition and removal
should be accompanied with refcount increment and decrement
respectively. Failing to do so synchronously leads to a race condition
that causes symptoms like use-after-free and memory corruption.
This commit:
 - makes existing session cache locking explicit, thus allowing
   individual engines to manage lock's scope.
 - fixes OpenSSL and SChannel engines by putting refcount management
   inside this lock's scope in relevant places.
 - adds these explicit locking calls to other engines that use
   sessionid cache to accommodate for this change. Note, however,
   that it is unknown whether any of these engines could also have
   this race.

Bug: https://github.com/curl/curl/issues/815
Fixes #815
Closes #847

Closes #822

... to make it not look like an OpenSSL function

Closes #844

This broke in 7.49.0 with commit e2000344

Fixes #842

Mostly in order to support broken web sites that redirect to broken URLs
that are accepted by browsers.

Browsers are typically even more leniant than this as the WHATWG URL
spec they should allow an _infinite_ amount. I tested 8000 slashes with
Firefox and it just worked.

Added test case 1141, 1142 and 1143 to verify the new parser.

Closes #791

Closes #837

Closes #838

Adds access to the effectively used http version to both libcurl and
curl.

Closes #799