contrib/wix/defines.wxi

verify: rename "hasmanifest" variable for source code readability

Before this patch, there are two ambiguous variables: "havemf" and
"hasmanifest".

"havemf" means whether there are any "manifest" entries.

"hasmanifest" means whether there are any "changelog" entries
referring to "manifest" entry.

This patch renames from "hasmanifest" to "refersmf" to clear
difference from "havemf".

<Include>

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

</Include>