url.c: use the preferred symbol name: *READDATA

with CURL_NO_OLDIES defined, it doesn't compile because this deprecated
symbol (*INFILE) is used

Bug: http://curl.haxx.se/bug/view.cgi?id=1398
CONNECT: Revert Curl_proxyCONNECT back to 7.29.0 design

This reverts commit cb3e6dfa3511 and instead fixes the problem
differently.

The reverted commit addressed a test failure in test 1021 by simplifying
and generalizing the code flow in a way that damaged the
performance. Now we modify the flow so that Curl_proxyCONNECT() again
does as much as possible in one go, yet still do test 1021 with and
without valgrind. It failed due to mistakes in the multi state machine.

Bug: http://curl.haxx.se/bug/view.cgi?id=1397
Reported-by: Paul Saab
curl_gssapi: Add macros for common mechs and pass them appropriately

Macros defined: KRB5_MECHANISM and SPNEGO_MECHANISM called from
HTTP, FTP and SOCKS on Unix
HTTP: Remove checkprefix("GSS-Negotiate")

That auth mech has never existed neither on MS nor on Unix side.
There is only Negotiate over SPNEGO.
configure/features: Add feature and version info for GSS-API and SPNEGO
curl.h/features: Deprecate GSS-Negotiate macros due to bad naming

- Replace CURLAUTH_GSSNEGOTIATE with CURLAUTH_NEGOTIATE
- CURL_VERSION_GSSNEGOTIATE is deprecated which
  is served by CURL_VERSION_SSPI, CURL_VERSION_GSSAPI and
  CURUL_VERSION_SPNEGO now.
- Remove display of feature 'GSS-Negotiate'
docs: Improve inline GSS-API naming in code documentation
http_negotiate: remove unused variable
test1013.pl: remove SPNEGO/GSS-API tweaks

No longer necessary after Michael Osipov's rework
symbols-in-versions: new SPNEGO/GSS-API symbols in 7.38.0
cyassl.c: return the correct error code on no CA cert

CyaSSL 3.0.0 returns a unique error code if no CA cert is available,
so translate that into CURLE_SSL_CACERT_BADFILE when peer verification
is requested.
http2: more and better error checking

1 - fixes the warnings when built without http2 support

2 - adds CURLE_HTTP2, a new error code for errors detected by nghttp2
basically when they are about http2 specific things.
RELEASE-NOTES: synced with 81cd24adb8b
conncache: fix compiler warning

warning C4267: '=' : conversion from 'size_t' to 'long', possible loss
of data

The member connection_id of struct connectdata is a long (always a
32-bit signed integer on Visual C++) and the member next_connection_id
of struct conncache is a size_t, so one of them should be changed to
match the other.

This patch the size_t in struct conncache to long (the less invasive
change as that variable is only ever used in a single code line).

Bug: http://curl.haxx.se/bug/view.cgi?id=1399
GSSAPI: private export mechanisms OIDs. OS400: Make RPG binding up to date.
findprotocol: show unsupported protocol within quotes

... to aid when for example prefixed with a space or other weird
character.
GSSAPI: remove useless *_MECHANISM defines.
libtest: fixed duplicated line in Makefile

Bug: https://github.com/bagder/curl/pull/105
test1013.pl: GSS-Negotiate doesn't exist as a feature anymore
symbols: CURL_VERSION_GSSNEGOTIATE is deprecated