Since WinSSL cannot be build without SSPI being enabled,
USE_WINSSL now defaults to the value of USE_SSPI.

The makefile does now raise an error if WinSSL is enabled
while SSPI is disabled.

Renamed external parameter USE_SSPI = yes/no to ENABLE_SSPI = yes/no.
Backwards compatible change: USE_SSPI can still be passed as external
parameter with yes/no value as long as ENABLE_SSPI is not given.

USE_x defines are passed around with true/false values internally,
USE_SSPI is now aligned to this approach, but still accepts external
values yes/no being passed, just like the other defines.

- Changed space usage to line up with the whole file
- Renamed CFLAGS_SSPI/IPV6 to SSPI/IPV6_CFLAGS to be
  consistent with the other CFLAGS_x variables
- Make use of existing CFLAGS_IPV6 (previously IPV6_CFLAGS)
  instead of appending directly to CFLAGS

The code was printing a warning when SNI was set up successfully. Oops.

Printing the cipher number in verbose mode was something only TLS/SSL
programmers might understand, so I had it print the name of the cipher,
just like in the OpenSSL code. That'll be at least a little bit easier
to understand. The SecureTransport API doesn't have a method of getting
a string from a cipher like OpenSSL does, so I had to generate the
strings manually.

Bug #75 updated with additional info, still remains for builds with
other backends.

Reduce the number of #ifdef UNICODE directives used in source files.

Test 1008 and 206 don't show the disconnect since it happens when SWS
awaits a new request, but 503 does and so the verify section needs that
string added.

When doing CONNECT requests, libcurl must make sure the connection is
alive as much as possible. NTLM requires it and it is generally good for
other cases as well.

NTLM over CONNECT requests has been broken since this regression I
introduced in my CONNECT cleanup commits that started with 41b02378,
included since 7.25.0.

Bug: http://curl.haxx.se/bug/view.cgi?id=3538625
Reported by: Marcel Raad

I moved out the servercmd parsing into a its own function called
parse_servercmd() and made sure it gets used also when the test number
is extracted from CONNECT requests. It turned out sws didn't do that
previously!

Using this, the server will output in the protocol log when the
connection gets disconnected and thus we will verify correctly in the
test cases that the connection doesn't get closed prematurely. This is
important for example NTLM to work.

Documentation added to FILEFORMAT, test 503 updated to use this.

Mention the CURL_SOCKET_TIMEOUT argument in step 6 of the typical
application.

Added function macros to make path converting easier.
Added CROSSPREFIX to all compile tools.

Posted by Marc Hoersken.

When compiling libcurl with UNICODE defined and using unicode characters
in username.

Enabling test2017 to test2022.

Currently it is unknown if there is any version of clang that
actually supports -Wstrict-aliasing. What is known is that there
are several that don't support it.