contrib/wix/defines.wxi

hgweb: wrap {branch} and {changesetbranch} by hybridlist()

This is also a 0/1-length list of a simple value, can be a hybrid list.
Appears that we have many {branch} variants.

<Include>

  <?if $(var.Platform) = "x64" ?>
    <?define IsX64 = yes ?>
  <?else?>
    <?define IsX64 = no ?>
  <?endif?>

</Include>