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.

With this commit, checks done in previous test2017 are now done in test2018.

Whole range test2017 to test2022 DISABLED until configure is capable of
requiring a new-enough metalink library.

Don't try these without mentioned check in place!

Print "parsing (...) OK" only when no warnings are generated.  If
no file is found in Metalink, treat it FAILED.

If no digest is provided, print WARNING in parse_metalink().
Also print validating FAILED after download.

These changes make tests 2012 to 2016 pass.