New revisions sometimes not shown in the index

[James Tait]

David Planella pinged me about the latest revision of his calculator app not showing up in search results. Investigation on the back-end Elasticsearch showed that there were indeed two package documents present, one each for revisions 1 and 2 of the package, and both had the `status` field set to "Published", but that somewhere along the way we've picked up an additional boolean field `is_published` which was `true` for revision 1, but `false` for revision 2, despite the content of the `status` field. Consequently, CPI was filtering revision 2 out as unpublished. A simple re-index of the package from SCA restored order, but there have been several instances of this problem.