Changes for compiling under MinGW-w64

Uses: GNU C compiler for MinGW-w64 targeting Win32

Tested with the meta-package gcc-mingw-w64-i686 under Debian Linux
(wheezy-stable and testing).

MinGW-w64 is a lot better but the generated makefile no longer works
without removing the -mno-cygwin flag. Also the features disabled in
the Makefile all seem to work for this version.

As it uses GCC I've also added -std=c90 per PuTTY policy.
(Only available for GCC >= 4.5)
Explicitly turn on nxcompat flag for cygwin

It seems that some 32bit versions don't use DEP without being asked.
Enable 64bit builds.
DEBUG messages for tracing
Windows: Extend the direct to font DBCS cursor.

If we're sitting on a DBCS lead byte it extends the cursor to two
characters rather then just one.

Priority: Low
Reconfigure PuTTY colour scheme from Unix host.

This is possibly related to: /wishlist/colour-scheme.html

These colour schemes are not stored in the PuTTY session file but are
instead "dynamically" configured from the host.

This script can send the required control sequences suitable for any
modern version of PuTTY or the Linux console.

It can calculate several standard forms and contains a default PuTTY
and XTerm mappings. In addition it can extract the colour scheme from
a Windows PuTTY registry dump, a Unix session file and a few other
file types.
Fixup for new PuTTY version scheme
Change C-S-Space keyboard mapping.

On Windows.
Generate a unicode no-break space for Ctrl-Shift-Space rather than byte 160
sent directly up the line to the server.
UnixGTK: Fix big cursor CSI sequence.

This enables the sequence "CSI 34 l" and "CSI 34 h" to allow the host
to switch the cursor to the big block (if it's currently the one of the
line cursors)

Windows already worked like this.
Windows stricmp and strnicmp are no longer supported.

Replace them with the standard strcasecmp and strncasecmp then add a
local implementation for libc's too broken to include them.