Ensure to clear the session object in case the libssh2 initialization
fails.

It could be argued that the libssh2 error function should be called to
get a proper error message in this case. But since the only error path
in libssh2_knownhost_init() is memory a allocation failure it's safest
to avoid since the libssh2 error handling allocates memory.

Closes #3179
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

... I'm moving it up one week due to travels. The rest stays.

Closes #3176

Detected by clang-tidy

Closes #3176

Fixes #3171
Closes #3172

Reported-by: Gisle Vanem
Bug: https://github.com/curl/curl/commit/becfe1233ff2b6b0c3e1b6a10048b55b68c2539f#commitcomment-31008819
Closes #3161

Reported-by: Dima Pasechnik
Fixes #3143
Closes #3174

Compiling on _WIN32 and with USE_LWIPSOCK, causes this error:
  curl_rtmp.c(223,3):  error: use of undeclared identifier 'setsockopt'
    setsockopt(r->m_sb.sb_socket, SOL_SOCKET, SO_RCVTIMEO,
    ^
  curl_rtmp.c(41,32):  note: expanded from macro 'setsockopt'
  #define setsockopt(a,b,c,d,e) (setsockopt)(a,b,c,(const char *)d,(int)e)
                                 ^
Closes #3155

Follow-up to #3166 which did the cmake part of this. This type/define is
not used.

Closes #3168

Remove variables:
* HAVE_SOCKLEN_T
* CURL_SIZEOF_CURL_SOCKLEN_T
* CURL_TYPEOF_CURL_SOCKLEN_T

Closes #3166

The "connecting" function is used by multiple protocols, not only FTP

- Change the inout parameters after all needed memory has been
  allocated. Do not change them if something goes wrong.
- Free the allocated temporary strings if strdup() fails.

Closes #3122

Closes #3162

lwIP on Windows does not have a WSAIoctl() function. 
But it do have a SO_SNDBUF option to lwip_setsockopt(). But it currently does nothing.

... by making the converter function global and accessible.

Closes #3153

Follow-up to 05564e75. This function no longer frees the passed-in
URL.

Reported-by: Michael Kaufmann
Bug: https://github.com/curl/curl/commit/05564e750e8f0c79016c680f301ce251e6e86155#commitcomm
ent-30985666

Most headerfiles end with a /* <headerguard> */ comment, but it was
missing from some. The comment isn't the most important part of our
code documentation but consistency has an intrinsic value in itself.
This adds header guard comments to the files that were lacking it.

Closes #3158
Reviewed-by: Jay Satiro <raysatiro@yahoo.com>
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

Closes https://github.com/curl/curl/pull/3159

Retract the previous approach as the sponsors will be the ones to set the
final amounts.

Closes #3152
[ci skip]

Curl_follow() no longer frees the string. Make sure it happens in the
caller function, like we normally handle allocations.

This bug was introduced with the use of the URL API internally, it has
never been in a release version

Reported-by: Dario Weißer
Closes #3149

Otherwise, closing that handle can still cause surprises!

Reported-by: Martin Ankerl
Fixes #3138
Closes #3147

The Visual Studio builds didn't use IPv6. Add it to all projects since
Visual Studio 2008, which is verified to build via AppVeyor.

Closes https://github.com/curl/curl/pull/3137

As done in the autotools and CMake builds by default.

Closes https://github.com/curl/curl/pull/3137

Closes #3144

Detected by Coverity.

Closes #3140
Reviewed-by: Jay Satiro

... now there's only BountyGraph.

For IP addresses in the subject alternative name field, the length
of the IP address (and hence the number of bytes to perform a
memcmp on) is incorrectly calculated to be zero. The code previously
subtracted q from name.end. where in a successful case q = name.end
and therefore addrlen equalled 0. The change modifies the code to
subtract name.beg from name.end to calculate the length correctly.

The issue only affects libcurl with GSKit SSL, not other SSL backends.
The issue is not a security issue as IP verification would always fail.

Fixes #3102
Closes #3141

Commit 57348eb9

 added support for the
MesaLink vtls backend, but missed updating the TLS section containing
supported backends in the docs.

Closes #3134
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

If USE_BLOCKING_SOCKETS is defined, curlx_nonblock's arguments are not
used.

Closes #3124

Ref: https://rawgit.com/ "RawGit has reached the end of its useful life"
Ref: https://news.ycombinator.com/item?id=18202481
Closes https://github.com/curl/curl/pull/3131

[ci skip]

and remove BOM from projects/wolfssl_override.props

Closes #3126

Accidentally aded in commit 1bb86057.

Reported-by: Viktor Szakats
Ref: https://github.com/curl/curl/pull/3120#issuecomment-428673136

- link TLS 1.2 and TLS 1.3 options
- link proxy and non-proxy options

Closes #3121

Removed in ae762e1a, accidentally added
again in 9f3be567.

As done in the autotools build. This is required for MinGW, which
supports only %I64 for printing 64-bit values, but warns about it.

Closes https://github.com/curl/curl/pull/3120