contrib/wix/defines.wxi

graft: use a real conflict for the tests

One of the graft tests grafts a changeset that changes a file's
content from 'a' to 'b' onto a branch that has changed the file's
content from 'a', via 'b', and then back to 'a' again. To prepare for
not considering this a file in need of merging, let's use 'c' as the
file's new content to make sure it has to be considered
conflicting.

There's a second similar case further down where an ancestor is
grafted. Make sure that is also considered a conflict.

<Include>

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

</Include>