Improve symlinks on Windows

This should avoid:
> Warning: symlink() : Could not fetch file information(error 3) ... in src\Local\Toolstack\ToolstackBase.php on line 106

and:
> Warning: unlink(C:\path\to/www): Permission denied ... in src\Local\Toolstack\Drupal.php on line 210

and:
> Warning: symlink(): Cannot create symlink, error code(183) in src\Local\Toolstack\Drupal.php on line 212

... but it doesn't solve the permission problem ("error 1314")