Hide .orgx files and use theindex.org directly.
Deleting .orgx files is an error -- thanks to Carsten for pointing
at this. Instead, we "hide" them by using dotted files: .file.orgx.
Also, use theindex.org directly instead of including theindex.inc in
theindex.org. This prevents a bug about republication of theindex.org
being skipped because the file has not been updated.
* org-publish.el (org-publish-index-generate-theindex): rename
from `org-publish-index-generate-theindex.inc'. Use the file
theindex.org directly instead of including theindex.inc.
(org-publish-projects): Don't delete .orgx files.
(org-publish-aux-preprocess): Use .file.orgx.