largefiles: allow to run 'debugupgraderepo' on repo with largefiles
The extensions wrap the necessary function to ensure the 'largefiles'
requirements won't be dropped.
It is now possible to run `hg debugupgraderepo` on a repository with largefiles.
<Include>
<?if $(var.Platform) = "x64" ?>
<?define IsX64 = yes ?>
<?else?>
<?define IsX64 = no ?>
<?endif?>
</Include>