Use and generate CURL_ZERO_TERMINATED in curl tool and tests.

To support telling a string is nul-terminated, symbol CURL_ZERO_TERMINATED
has been introduced.

Documentation updated accordingly.

symbols in versions updated. Added form API symbols deprecation info.

This feature is badly supported in Windows: as a replacement, a caller has
to use curl_mime_data_cb() with fread, fseek and possibly fclose
callbacks to process opened files.

The cli tool and documentation are updated accordingly.

The feature is however kept internally for form API compatibility, with
the known caveats it always had.

As a side effect, stdin size is not determined by the cli tool even if
possible and this results in a chunked transfer encoding. Test 173 is
updated accordingly.

Additional mime-specific tests.
Existing tests updated to reflect small differences (Expect: 100-continue,
data size change due to empty lines, etc).
Option -F headers= keyword added to tests.
test1135 disabled until the entry point order change is resolved.
New example smtp-mime.
Examples postit2 and multi-post converted from form API to mime API.

Extended -F option syntax to support multipart mail messages.
-F keyword headers= added to include custom headers in parts.
Documentation upgraded.

Available in HTTP, SMTP and IMAP.
Deprecates the FORM API.
See CURLOPT_MIMEPOST.
Lib code and associated documentation.

Shell profile output makes the SSH server failing and this problem reason
is not easy to find when no hint is given.

The case keyword may be followed by a constant expression and thus should
allow it to start with an open parenthesis.

This enables tests to create more than one file on the client side.

This will allow substitution of boundaries in mail messages.

Some calls in different modules were setting the data handle to NULL, causing
segmentation faults when using builds that enable character code conversions.

Automake gets confused if you want to use C++ static libraries with C
code - basically we need to involve the clang++ linker. The easiest way
of achieving this is to rename the C code as C++ code. This gets us a
bit further along the path and ought to be compatible with Google's
version of clang.

Closes #1849

Create simple seed corpora for:
- FTP
- telnet
- dict
- tftp
- imap
- pop3

based off the tests of the same number.

Closes #1842

- Start with the basic code from the ossfuzz project.
- Rewrite fuzz corpora to be binary files full of Type-Length-Value
  data, and write a glue layer in the fuzzing function to convert
  corpora into CURL options.
- Have supporting functions to generate corpora from existing tests
- Integrate with Makefile.am

... so that users can actually write code based on the man page alone,
not having to read the header file.

- Fix handling certificate subjects that are already UTF-8 encoded.

Follow-up to b3b75d17 from two days ago. Since then a copy would be
skipped if the subject was already UTF-8, possibly resulting in a NULL
deref later on.

Ref: https://github.com/curl/curl/issues/1823
Ref: https://github.com/curl/curl/pull/1831

Closes https://github.com/curl/curl/pull/1836

... instead of cyassl, as this is the current name for it.

Closes #1844

Reported-by: Dan Fandrich
Bug: https://curl.haxx.se/mail/lib-2017-08/0121.html
Closes #1843

... when darwinssl is used.

Reported-by: Viktor Szakats
Bug: https://github.com/curl/curl/commit/b0989cd3abaff4f9a0717b4875022fa79e33b481#commitcomment-23943493

Closes #1845

./sslbackend.c:58:3: warning: else after closing brace on same line (BRACEELSE)
   } else if(isdigit(*name)) {
   ^
./sslbackend.c:62:3: warning: else after closing brace on same line (BRACEELSE)
   } else
   ^

Closes https://github.com/curl/curl/pull/1840

The CURLSSLBACKEND_WOLFSSL is supposed to be an alias for
CURLSSLBACKEND_CYASSL, but used an erronous value. To reduce the risk
for a similar mistake, define the backend aliases to use the enum values
instead.

Reported-by: Gisle Vanem
Bug: https://curl.haxx.se/mail/lib-2017-08/0120.html

it is a one time *set*, not necessarily a one time use... it can be
called again if the first call failed or just listed the alternatives.

clarify that the available backends are the ones this build supports

plus add some formatting

Reported-by: Rich Gray
Bug: https://curl.haxx.se/mail/lib-2017-08/0119.html

Regression since 1328f69d

Fixes #1841
Reported-by: Andrei Karas

Closes #1837

destroy_async_data() assumes that if the flag "done" is not set yet, the
thread itself will clean up once the request is complete.  But if an
error (generally OOM) occurs before the thread even has a chance to
start, it will never get a chance to clean up and memory will be leaked.
By clearing "done" only just before starting the thread, the correct
cleanup sequence will happen in all cases.

This used to be set in some configurations to EAI_MEMORY which is not a
valid value for errno and caused Curl_strerror to fail an assertion.

There is a mode in which libcurl is compiled with versioned symbols,
depending on the active SSL backend.

When multiple SSL backends are active, it does not make sense to favor
one over the others, so let's not: introduce a new prefix for the case
where multiple SSL backends are compiled into cURL.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>