Detected by test 1132

When building the code using LLVM Clang without NGHTTP2, I was getting
this warning:
../lib/http.h:155:1: warning: empty struct is a GNU extension [-Wgnu]
Placing a dummy variable into the data structure silenced the warning.

Since it now actually says if 1.1 or a later version should be used.

Recent OpenSSL uses user interface abstraction to negotiate access to
private keys in the cryprographical engines. An OpenSSL application is
expected to implement the user interface. Otherwise a default one
provided by OpenSSL (interactive standard I/O) will be used and the
aplication will have no way how to pass a password to the engine.

Longer-desc: http://curl.haxx.se/mail/lib-2013-08/0265.html

Using the first little merge of nghttp2 into libcurl, I stumbeled on the
missing 'snprintf' in MSVCRT. Isn't this how we do it for other libcurl
files?  I.e. use 'curl_msnprintf' and not 'snprintf' directly:

When an error occurs parsing an LDAP URL, The ludp->lud_attrs[i] entries
could be freed even though they sometimes point to data within an
allocated area.

This change introduces a lud_attrs_dup[] array for the duplicated string
pointers, and it removes the unused lud_exts array.

Bug: http://curl.haxx.se/mail/lib-2013-08/0209.html

I also documented the fact that the OpenSSL engine also supports them.

comparison between signed and unsigned integer expressions

suggest parentheses around '&&' within '||' (twice)

XOAUTH2 would be selected in preference to LOGIN and PLAIN if the IMAP
or SMTP server advertised support for it even though a user's password
was supplied but bearer token wasn't.

Modified the selection logic so that XOAUTH2 will only be selected if
the server supports it and A) The curl user/libcurl programmer has
specifically asked for XOAUTH via the ;AUTH=XOAUTH login option or 2)
The bearer token is specified. Obviously if XOAUTH is asked for via
the login option but no token is specified the user will receive a
authentication failure which makes more sense than no known
authentication mechanisms supported!

Initial library considerations documented in lib/README.http2

An enumerated type is mixed with another type

warning: `code' might be used uninitialized in this function

... when doing upload it would return the wrong values at times. This
commit attempts to cleanup the mess.

Bug: http://curl.haxx.se/mail/lib-2013-08/0109.html
Reported-by: Mike Mio

When removing an already removed handle, avoid that to ruin the
internals and just return OK instead.

'struct monitor', introduced in 6cf8413e, already exists in an IRIX
header file (sys/mon.h) which gets included via various standard headers
by lib/easy.c

cc-1101 cc: ERROR File = ../../curl/lib/easy.c, Line = 458
"monitor" has already been declared in the current scope.

Reported-by: Tor Arntsen

When waiting for a 100-continue response from the server, the
Curl_readwrite() will refuse to run if called until the timeout has been
reached.

We timeout code in multi_socket() allows code to run slightly before the
actual timeout time, so for test 154 it could lead to the function being
executed but refused in Curl_readwrite() and then the application would
just sit idling forever.

This was detected with runtests.pl -e on test 154.

I brought back security.h in commit bb552933. As we actually
already found out back in 2005 in commit 62970da6, the file name
security.h causes problems so I renamed it curl_sec.h instead.

Added the ability to use an XOAUTH2 bearer token [RFC6750] with SMTP for
authentication using RFC6749 "OAuth 2.0 Authorization Framework".

The bearer token is expected to be valid for the user specified in
conn->user. If CURLOPT_XOAUTH2_BEARER is defined and the connection has
an advertised auth mechanism of "XOAUTH2", the user and access token are
formatted as a base64 encoded string and sent to the server as
"AUTH XOAUTH2 <bearer token>".

Added the ability to use an XOAUTH2 bearer token [RFC6750] with IMAP for
authentication using RFC6749 "OAuth 2.0 Authorization Framework".

The bearer token is expected to be valid for the user specified in
conn->user. If CURLOPT_XOAUTH2_BEARER is defined and the connection has
an advertised auth mechanism of "XOAUTH2", the user and access token are
formatted as a base64 encoded string and sent to the server as
"A001 AUTHENTICATE XOAUTH2 <bearer token>".

ISO C forbids forward references to 'enum' types

Added the ability to specify an XOAUTH2 bearer token [RFC6750] via the
option CURLOPT_XOAUTH2_BEARER for authentication using RFC6749 "OAuth
2.0 Authorization Framework".

Added the ability to generated a base64 encoded XOAUTH2 token
containing: "user=<username>^Aauth=Bearer <bearer token>^A^A"
as per RFC6749 "OAuth 2.0 Authorization Framework".

We've announced this pending removal for a long time and we've
repeatedly asked if anyone would care or if anyone objects. Nobody has
objected. It has probably not even been working for a good while since
nobody has tested/used this code recently.

The stuff in krb4.h that was generic enough to be used by other sources
is now present in security.h

Make sure we always return CURLM_CALL_MULTI_PERFORM when we reach
CURLM_STATE_DONE since the state is transient and it can very well
continue executing as there is nothing to wait for.

Bug: http://curl.haxx.se/mail/lib-2013-08/0211.html
Reported-by: Yi Huang

... this also makes sure that the progess callback gets called more
often during TFTP transfers.

Added test 1238 to verify.

Bug: http://curl.haxx.se/bug/view.cgi?id=1269
Reported-by: Jo3

I build curl.exe (using MingW) with '-DCURLDEBUG' and by importing from
libcurl.dll.  Which means the new curl_easy_perform_ev() must be
exported from libcurl.dll.

Doing curl_multi_add_handle() on an easy handle that is already added to
a multi handle now returns this error code. It previously returned
CURLM_BAD_EASY_HANDLE for this condition.

The closure_handle is "owned" by the multi handle and it is
unconditional so the setting up of it should be in the Curl_multi_handle
function rather than curl_multi_add_handle.

As it is done unconditionally in multi_init() this code will never run!

This function is meant to work *exactly* as curl_easy_perform() but will
use the event-based libcurl API internally instead of
curl_multi_perform(). To avoid relying on an actual event-based library
and to not use non-portable functions (like epoll or similar), there's a
rather inefficient emulation layer implemented on top of Curl_poll()
instead.

There's currently some convenience logging done in curl_easy_perform_ev
which helps when tracking down problems. They may be suitable to remove
or change once things seem to be fine enough.

curl has a new --test-event option when built with debug enabled that
then uses curl_easy_perform_ev() instead of curl_easy_perform(). If
built without debug, using --test-event will only output a warning
message.

NOTE: curl_easy_perform_ev() is not part if the public API on purpose.
It is only present in debug builds of libcurl and MUST NOT be considered
stable even then. Use it for libcurl-testing purposes only.

runtests.pl now features an -e command line option that makes it use
--test-event for all curl command line tests. The man page is updated.