MesaLink support was added in commit 57348eb9

 but the
backend was never added to the curl_sslbackend enum in curl/curl.h.
This adds the new backend to the enum and updates the relevant docs.

Closes #3195
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

Closes #3191

CVE-2018-16842
Reported-by: Brian Carpenter
Bug: https://curl.haxx.se/docs/CVE-2018-16842.html

Closes #3123

Detected by UndefinedBehaviorSanitizer

Closes #3187

Closes #3182

Closes #3186

CVE-2018-16839
Reported-by: Harry Sintonen
Bug: https://curl.haxx.se/docs/CVE-2018-16839.html

Regression from b46cfbc0 (7.59.0)
CVE-2018-16840
Reported-by: Brian Carpenter (Geeknik Labs)

Bug: https://curl.haxx.se/docs/CVE-2018-16840.html

system.h selects the proper Sun settings when __SUNPRO_C is defined. The
Sun compiler does not define it when compiling C++ files.  I'm adding a
check also on __SUNPRO_CC to allow curl to work properly also when used
in a C++ project on Sun Solaris.

Closes #3181

The version used for Gskit, NSS, GnuTLS, WolfSSL and schannel.

Available in the root, src and lib dirs.

Closes #3163

See: https://curl.haxx.se/mail/lib-2018-10/0107.html

Use an unsigned variable: as the signed operation behavior is undefined,
this change silents clang-tidy about it.

Ref: https://github.com/curl/curl/pull/3163
Reported-By: Daniel Stenberg

If Curl_protocol_connect() returns an error code,
handle the error instead of switching to the next state.

Closes #3170

When failing to set the 1.3 cipher suite, the wrong string pointer would
be used in the error message. Most often saying "(nil)".

Reported-by: Ricky-Tigg on github
Fixes #3178
Closes #3180

... picked straight from the OpenSSL man page:
https://www.openssl.org/docs/manmaster/man3/SSL_CTX_set_ciphersuites.html

Reported-by: Ricky-Tigg on github
Bug: #3178

This is required for gnutls-serv, which enables a few more tests.

Closes https://github.com/curl/curl/pull/2958

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.