Update windows build documentation

Update windows build documentation

Mention Win7 in a few more places, and talk about VS 2010/2012.
I've had the best results with VS 2005, though.

Update dead URLs.

The old version of WiX 2.0 no longer seems available (at least not from
the listed URL); replace it with

Remove coverage of NSIS installers.

Update example OpenAFS version to 1.7.25.

De-emphasize VS 2003.

Update some ntbuild.bat settings and comments to be more useful and valid.

Change-Id: Iee305833e6d2b01dd7995a78863327682fe5a8eb
Reviewed-on: http://gerrit.openafs.org/10029
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>