Follow-up to commit 5eb2396c as that wasn't complete.

At times HEADERFUNCTION+HEADERDATA was set only to have only HEADERDATA
set in the subsequent loop which could cause a NULL to get sent as
userdata to 'header_callback' which wasn't made to handle that.

Now HEADERFUNCTION is explicitly set to NULL if it isn't set to the
callback.

Fix macro definition

Calling of curl_memdebug() was still done with a pending free()

As I modified conn->bits.tcpconnect to become an array that holds one
bool for each potential connection all uses of that struct field must
index it correctly.

When connecting, make sure TIMER_CONNECT is set.

When using the multi interface, a SOCKS proxy, and a connection that
wouldn't immediately consider itself connected (which my Linux tests do
by default), libcurl would be tricked into doing _two_ connects to the
SOCKS proxy when it setup the data connection and then of course the
second attempt would fail miserably and cause error.

This problem is a regression that was introduced by commit
4a42e5cd that was introduced in the 7.21.7 release.

Bug: http://curl.haxx.se/mail/lib-2011-08/0199.html
Reported by: Fabian Keil

Until 2011-08-17 libcurl's Memory Tracking feature also performed
automatic malloc and free filling operations using 0xA5 and 0x13
values. Our own preinitialization of dynamically allocated memory
might be useful when not using third party memory debuggers, but
on the other hand this would fool memory debuggers into thinking
that all dynamically allocated memory is properly initialized.

As a default setting, libcurl's Memory Tracking feature no longer
performs preinitialization of dynamically allocated memory on its
own. If you know what you are doing, and really want to retain old
behavior, you can achieve this compiling with preprocessor symbols
CURL_MT_MALLOC_FILL and CURL_MT_FREE_FILL defined with appropriate
values.

"release-ssl-ssh2-zlib" and "debug-ssl-ssh2-zlib" are two new makefile
targets that build libcurl with MSVC and link with libssh2

Bug: http://curl.haxx.se/bug/view.cgi?id=3388920
Reported by: "kdekker"

Two problems were fixed:

GET_PARAMETER responses that have no body must be 204 response or
properly set length to 0.

One of the <data> sections had the wrong content-length for its
GET_PARAMETER response.

Enabled test 572 again.

As bug 3385258 pointed out but I missed up the fix for. This is another
take at a fix.

Bug: http://curl.haxx.se/bug/view.cgi?id=3392101
Reported by: Wu Yongzheng

IRIX 6.5.24 gcc 3.3 autobuilds fail unittests library compilation due to a
problem related with OpenSSL headers and library versions not matching.

All AIX autobuilds fails unit tests linking against unittests library due to
unittests library being built with no symbols or members. Libtool ?

Bug: https://bugzilla.redhat.com/728562

Added comments to some remaining issues

Summary of the issue can be found at:
http://curl.haxx.se/mail/lib-2010-04/0367.html

That patch only updated the unix sockets code - the winsock code was not
updated and no longer works the same was as the unix code. This change
updates the windows code accordingly.

Bug: http://curl.haxx.se/bug/view.cgi?id=3163118

291 - bug 3383692 "GET PARAMETER request and body in response"

Inclusion of header "memdebug.h" in http_ntlm.c got lost in commit 98fb0ef7.

Bug: http://curl.haxx.se/bug/view.cgi?id=3383692

Strict splitting of http_ntlm.[ch] may trigger 8 compiler warnings when
building with some compilers and strict compiler warnings enabled, depending
on other specific configuration options some could get triggered or not.

Seven are related with 'unused function parameters' and another one with
'var may be used before its value is set'.

For modularity purposes, huge chunks of NTLM existing code is transformed into
functions to allow future internal code reuse.

Resulting three new libcurl private functions:

 - Curl_ntlm_create_type1_message()
 - Curl_ntlm_create_type3_message()
 - Curl_ntlm_decode_type2_message()

Changing static ntlm_sspi_cleanup() into non-static Curl_ntlm_sspi_cleanup()

This 'refactoring' has been prepared by previous commits to allow that this
specific one does not introduce any change to existing code. All existing
goodness and badness previous to this commit should remain the same once it is
applied, the only difference should be that existing code is moved into
functions.

Given the quite big portions of code being moved around, and the importance of
change traceability, this commit has been done in such a way that it is
possible to perform a three-way diff from initial http_ntlm.[ch] to resulting
http_ntlm.[ch] and curl_ntlm.[ch] to actually verify that no functional change
is introduced here.

Notice that Steve Holme has provided several patches, but these included this
refactoring along with 'extra' fixes. I really wanted this 'clean' refactoring
done first, in order to allow discussion or committing of 'extra' fixes on a
case by case basis, so, I had to bite the bullet ;-)

Comments, line adjustments, compiler warning fixes, whatever, may follow
afterwards.

warning C4706: assignment within conditional expression

Remove CURLntlm enum, no longer required.

Three more bugs fixed, three more contributors mentioned

Just a note about the fact that all VC[6/8/9/10] makefiles are generated
from the VC6 one as source.

When building on Windows, with CMake and mingw, curl fails to compile
because the CMake build system is not properly looking for the Winsock
libraries

Patch by: Pau Garcia i Quiles
Bug: http://curl.haxx.se/bug/view.cgi?id=3389231

Curl_readrewind() was called without checking its return code, which
could lead to badness.

Bug: http://curl.haxx.se/bug/view.cgi?id=3349227

Using this option with an argument being set to one of
none/policy/always instructs libcurl how to deal with GSS
credentials. Or rather how it tells the server that delegation is fine
or not.