Use a top-to-bottom numbering scheme for generating ids of subheadings and terms...

Use a top-to-bottom numbering scheme for generating ids of subheadings and terms. This scheme fixes permalinks to distinguish between items that would previously have the same ID attribute.

Where possible the generated ID values are the same as those generated with the previous versions of the stylesheet
to retain backwards compatibility with published links.

As a side effect of the changes xsltproc should no longer complain about duplicate IDs during build.