A libssh2 library in the standard system location was being used in
preference to the desired one while linking.

Add the new option CURLOPT_KEEP_SENDING_ON_ERROR to control whether
sending the request body shall be completed when the server responds
early with an error status code.

This is suitable for manual NTLM authentication.

Reviewed-by: Jay Satiro

Closes https://github.com/curl/curl/pull/904

As it seems to be a rarely used cipher suite (for securely established
but _unencrypted_ connections), I believe it is fine not to provide an
alias for the misspelled variant.

.. and add that --proto-redir and CURLOPT_REDIR_PROTOCOLS do not
override protocols denied by --proto and CURLOPT_PROTOCOLS.

- Add a test to enforce: --proto deny must override --proto-redir allow

Closes https://github.com/curl/curl/pull/1031

Follow-up to 6140dfcf

Reported-by: Alexander Sinditskiy

Discussed in #997

Assisted-by: Jay Satiro

Bug: https://github.com/curl/curl/issues/1017
Reported-by: Jeroen Ooms

Closes https://github.com/curl/curl/pull/1028

LibreSSL defines `OPENSSL_VERSION_NUMBER` as `0x20000000L` for all
versions returning `LibreSSL/2.0.0` for any LibreSSL version.

This change provides a local OpenSSL_version_num function replacement
returning LIBRESSL_VERSION_NUMBER instead.

Closes #1029

Closes #1025
Closes #1026
Closes #1027

Follow-up fix to d9321562

The OpenSSL function CRYTPO_cleanup_all_ex_data() cannot be called
multiple times without crashing - and other libs might call it! We
basically cannot call it without risking a crash. The function is a
no-op since OpenSSL 1.1.0.

Not calling this function only risks a small memory leak with OpenSSL <
1.1.0.

Bug: https://curl.haxx.se/mail/lib-2016-09/0045.html
Reported-by: Todd Short

RC4 was a nice alternative to CBC back in the days of BEAST, but it's insecure and obsolete now.

Since I first wrote that text, Apple introduced tvOS and watchOS, and renamed "Mac OS X" to "macOS." Let's make the text a little more inclusive, since curl can be built for all four operating systems.

Prior to this commit this example failed with error
'Cannot APPEND with unknown input file size'.

Bug: https://github.com/curl/curl/issues/1008


Reported-by:  <lukaszgn@users.noreply.github.com>

Closes https://github.com/curl/curl/pull/1011

Recent versions of mbedTLS are available under either Apache 2.0 or GPL
2.0, see https://tls.mbed.org/how-to-get

Closes #1019

... but don't send the actual header over the wire as it isn't accepted.
Chunked uploading is still triggered using this method.

Fixes #1013
Fixes #662

OpenSSL 1.0.1 and 1.0.2 build an error queue that is stored per-thread
so we need to clean it when easy handles are freed, in case the thread
will be killed in which the easy handle was used. All OpenSSL code in
libcurl should extract the error in association with the error already
so clearing this queue here should be harmless at worst.

Fixes #964

CVE-2016-7167

Bug: https://curl.haxx.se/docs/adv_20160914.html

CVE-2016-7167

Bug: https://curl.haxx.se/docs/adv_20160914.html

Reported-by: Ryan Scott

Fixes #1007

NTLM support with mbedTLS was added in 497e7c9d but requires that mbedTLS
is built with the MD4 functions available, which it isn't in default
builds. This now adapts if the funtion isn't there and builds libcurl
without NTLM support if so.

Fixes #1004

- Change maximum allowed line length from 80 to 79.

Note that since the added examples are for column alignment I had to
encapsulate with ~~~c markdown to preserve their alignment.