This error code was once introduced when some library was dynamically
loaded and a funciton within said library couldn't be found.

CURLOPT_SOCKS_PROXY -> CURLOPT_PRE_PROXY

Added the corresponding --preroxy command line option. Sets a SOCKS
proxy to connect to _before_ connecting to a HTTP(S) proxy.

This was added as part of the SOCKS+HTTPS proxy merge but there's no
need to support this as we prefer to have the protocol specified as a
prefix instead.

In order to make the code style more uniform everywhere

Closes #1142

Adds access to the effectively used protocol/scheme to both libcurl and
curl, both in string and numeric (CURLPROTO_*) form.

Note that the string form will be uppercase, as it is just the internal
string.

As these strings are declared internally as const, and all other strings
returned by curl_easy_getinfo() are de-facto const as well, string
handling in getinfo.c got const-ified.

Closes #1137

* HTTPS proxies:

An HTTPS proxy receives all transactions over an SSL/TLS connection.
Once a secure connection with the proxy is established, the user agent
uses the proxy as usual, including sending CONNECT requests to instruct
the proxy to establish a [usually secure] TCP tunnel with an origin
server. HTTPS proxies protect nearly all aspects of user-proxy
communications as opposed to HTTP proxies that receive all requests
(including CONNECT requests) in vulnerable clear text.

With HTTPS proxies, it is possible to have two concurrent _nested_
SSL/TLS sessions: the "outer" one between the user agent and the proxy
and the "inner" one between the user agent and the origin server
(through the proxy). This change adds supports for such nested sessions
as well.

A secure connection with a proxy requires its own set of the usual SSL
options (their actual descriptions differ and need polishing, see TODO):

  --proxy-cacert FILE        CA certificate to verify peer against
  --proxy-capath DIR         CA directory to verify peer against
  --proxy-cert CERT[:PASSWD] Client certificate file and password
  --proxy-cert-type TYPE     Certificate file type (DER/PEM/ENG)
  --proxy-ciphers LIST       SSL ciphers to use
  --proxy-crlfile FILE       Get a CRL list in PEM format from the file
  --proxy-insecure           Allow connections to proxies with bad certs
  --proxy-key KEY            Private key file name
  --proxy-key-type TYPE      Private key file type (DER/PEM/ENG)
  --proxy-pass PASS          Pass phrase for the private key
  --proxy-ssl-allow-beast    Allow security flaw to improve interop
  --proxy-sslv2              Use SSLv2
  --proxy-sslv3              Use SSLv3
  --proxy-tlsv1              Use TLSv1
  --proxy-tlsuser USER       TLS username
  --proxy-tlspassword STRING TLS password
  --proxy-tlsauthtype STRING TLS authentication type (default SRP)

All --proxy-foo options are independent from their --foo counterparts,
except --proxy-crlfile which defaults to --crlfile and --proxy-capath
which defaults to --capath.

Curl now also supports %{proxy_ssl_verify_result} --write-out variable,
similar to the existing %{ssl_verify_result} variable.

Supported backends: OpenSSL, GnuTLS, and NSS.

* A SOCKS proxy + HTTP/HTTPS proxy combination:

If both --socks* and --proxy options are given, Curl first connects to
the SOCKS proxy and then connects (through SOCKS) to the HTTP or HTTPS
proxy.

TODO: Update documentation for the new APIs and --proxy-* options.
Look for "Added in 7.XXX" marks.

Fully implemented with the NSS backend only for now.

Reviewed-by: Ray Satiro

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

Since we're using CURLE_FTP_WEIRD_SERVER_REPLY in imap, pop3 and smtp as
more of a generic "failed to parse" introduce an alias without FTP in
the name.

Closes https://github.com/curl/curl/pull/975

Many applications assume the actual contents of the public types and use
that do for example forward declarations (saving them from including our
public header) which then breaks when we switch from void * to a struct
*.

I'm not convinced we were wrong, but since this practise seems
widespread enough I'm willing to (partly) step down.

Now libcurl uses the struct itself when it is built and it allows
applications to use the struct type if CURL_STRICTER is defined at the
time of the #include.

Reported-by: Peter Frühberger
Fixes #926

Instead of typedef'ing to void, typedef to their corresponding actual
struct names to allow compilers to type-check.

Assisted-by: Reinhard Max

Adds access to the effectively used http version to both libcurl and
curl.

Closes #799

The preprocessor check that sets up the 32bit defines for non-configure
builds didn't work properly for MIPS systems as __mips__ is defined for
both 32bit and 64bit. Now __LP64__ is also checked and indicates 64bit.

Reported-by: Tomas Jakobsson
Fixes #813

Makes curl connect to the given host+port instead of the host+port found
in the URL.

Previously, when a stream was closed with other than NGHTTP2_NO_ERROR
by RST_STREAM, underlying TCP connection was dropped.  This is
undesirable since there may be other streams multiplexed and they are
very much fine.  This change introduce new error code
CURLE_HTTP2_STREAM, which indicates stream error that only affects the
relevant stream, and connection should be kept open.  The existing
CURLE_HTTP2 means connection error in general.

Ref: https://github.com/curl/curl/issues/659
Ref: https://github.com/curl/curl/pull/663

As these two options provide identical functionality, the former for
SOCK5 proxies and the latter for HTTP proxies, merged the two options
together.

As such CURLOPT_SOCKS5_GSSAPI_SERVICE is marked as deprecated as of
7.49.0.

So that we only do the extra typedefs in curl_memory.h when we really
need to and avoid double typedefs.

follow-up commit to 7218b52c

Thanks-to: Steve Holme

The define is not in our name space and is therefore not protected by
our API promises.

It was only really used by libcurl internals but was mostly erased from
there already in 8aabbf5f (March 2015). This is supposedly the final
death blow to that define from everywhere.

As a side-effect, making sure _MPRINTF_REPLACE is gone and not used, I
made the lib tests in tests/libtest/ use curl_printf.h for its redefine
magic and then subsequently the use of sprintf() got banned in the tests
as well (as it is in libcurl internals) and I then replaced them all
with snprintf().

In the unlikely event that any users is actually using this define and
gets sad by this change, it is very easily copied to the user's own
code.

Supports HTTP/2 over clear TCP

- Optimize switching to HTTP/2 by removing calls to init and setup
before switching. Switching will eventually call setup and setup calls
init.

- Supports new version to “force” the use of HTTP/2 over clean TCP

- Add common line parameter “--http2-prior-knowledge” to the Curl
  command line tool.