.. because functionality may be affected if the versions differ.

This commit implements TODO 18.7 "warning if curl version is not in sync
with libcurl version".

Ref: https://github.com/curl/curl/blob/curl-7_64_1/docs/TODO#L1028-L1033

Closes https://github.com/curl/curl/pull/3774

Following 28f826b3 to return CURLE_OK instead of numeric 0.

Make sure to run curl_global_cleanup() when shutting down the test
suite to release any resources allocated in the SSL setup. This is
clearly visible when running tests with PolarSSL where the thread
lock calloc() memory which isn't released when not running cleanup.
Below is an excerpt from the autobuild logs:

  ==12368== 96 bytes in 1 blocks are possibly lost in loss record 1 of 2
  ==12368== at 0x4837B65: calloc (vg_replace_malloc.c:752)
  ==12368== by 0x11A76E: curl_dbg_calloc (memdebug.c:205)
  ==12368== by 0x145CDF: Curl_polarsslthreadlock_thread_setup
                         (polarssl_threadlock.c:54)
  ==12368== by 0x145B37: Curl_polarssl_init (polarssl.c:865)
  ==12368== by 0x14129D: Curl_ssl_init (vtls.c:171)
  ==12368== by 0x118B4C: global_init (easy.c:158)
  ==12368== by 0x118BF5: curl_global_init (easy.c:221)
  ==12368== by 0x118D0B: curl_easy_init (easy.c:299)
  ==12368== by 0x114E96: test (lib1906.c:32)
  ==12368== by 0x115495: main (first.c:174)

Closes #3783
Reviewed-by: Marcel Raad <Marcel.Raad@teamviewer.com>
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

No need to build it from source anymore.

Closes https://github.com/curl/curl/pull/3779

This makes building libpsl and libidn2 from source unnecessary and
removes the need for the autopoint and libunistring-dev packages.

Closes https://github.com/curl/curl/pull/3779

... without a $srcdir prefix. Triggered by the failures in several
autobuilds.

Closes #3781

Reviewed-by: Daniel Stenberg <daniel@haxx.se>

Mark global variables static to avoid compiler warning in Clang when
using -Wmissing-variable-declarations.

Closes #3778
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

The indentation from 211d5329 and 57d6d253 was a little strange as
parts didn't align correctly, uses 4 spaces rather than 2. Checked
the indentation of the original source so it aligns, albeit, using
curl style.

Xenial comes with more up-to-date software versions and more available
packages, some of which we currently build from source. Unfortunately,
some builds would fail with Xenial because of assertion failures in
Valgrind when using OpenSSL, so leave these at Trusty.

Closes https://github.com/curl/curl/pull/3777

Make all SOCKS tests use socksd instead of ssh.

Closes #3752

To aid debugging better.

Commit 9081014c fixed most of the confusing issues between scope id and
scope however 844896d0 added bad limits checking assuming that the scope
is being set and not the scope id.

I have fixed the documentation so it all refers to scope ids.

In addition Curl_if2ip refered to the scope id as remote_scope_id which
is incorrect, so I renamed it to local_scope_id.

Adjusted-by: Daniel Stenberg

Closes #3655
Closes #3765
Fixes #3713

Only allow well formed decimal numbers in the input.

Document that the number MUST be between 1 and 65535.

Add tests to test 1560 to verify the above.

Ref: https://github.com/curl/curl/issues/3753
Closes #3762

- Remove the lines in winbuild/Makefile.vc that generate an error with
  multiple SSL backends.

- Add /DCURL_WITH_MULTI_SSL in winbuild/MakefileBuild.vc if multiple SSL
  backends are set.

Closes https://github.com/curl/curl/pull/3772

Since the mesalink build started to fail on travis, even though we build
a fixed release version, we disable it to prevent it from blocking
progress.

Closes #3767

Without this, detecting and avoid reusing a closed TLS connection
(without a previous GOAWAY) when doing HTTP/2 is tricky.

Reported-by: Tom van der Woerdt
Fixes #3750
Closes #3763

Functionally this doesn't change anything as we still use the username
for both the authorisation identity and the authentication identity.

Closes #3757

Based-on-code-by: Poul T Lomholt

Since a few code paths actually update that data.

Fixes #3753
Closes #3761

Reported-by: Poul T Lomholt

Remove the code too. The functionality has been disabled in code since
7.62.0. Setting this option will from now on simply be ignored and have
no function.

Closes #3654

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

Reduces the time needed for the other jobs a little.

Closes https://github.com/curl/curl/pull/3721

This reduces the GCC job runtimes a little and it's needed to
selectively update clang builds to xenial.

Closes https://github.com/curl/curl/pull/3721

Closes https://github.com/curl/curl/pull/3725

- remove unused variables
- declare conditionally used variables conditionally
- suppress unused variable warnings in the CMake tests
- remove dead variable stores
- consistently use WIN32 macro to detect Windows

Closes https://github.com/curl/curl/pull/3739

Make functions no-ops if neither both USE_THREADS_POSIX and
HAVE_PTHREAD_H nor both USE_THREADS_WIN32 and HAVE_PROCESS_H are
defined. Previously, if only one of them was defined, there was either
code compiled that did nothing useful or the wrong header included for
the functions used.

Also, move POLARSSL_MUTEX_T define to implementation file as it's not
used externally.

Closes https://github.com/curl/curl/pull/3739

These variables are only conditionally initialized.

Closes https://github.com/curl/curl/pull/3739

Closes https://github.com/curl/curl/pull/3739