This is an old revision of the document!

---

This page links to a preliminary version of a paper in preparation for a journal. It is too preliminary for even preliminary publication now; it will be submitted to arxiv once results are more complete (espected to be two to three weeks), but the background material is required for a paper currently in review, so this version is provided for that purpose only. By clicking on this link to download the paer, you agree to delete this preliminary draft once a public version is made available on arxiv (a link to the arxiv paper will be placed here).