Add special handling of the DocBook trademark tag.

Each trademark will only have a trademark symbol appended the first
time in a document for print / html, and the first time on each HTML
page for html-split.

It is possible to always append the trademark symbol for a trademark,
by setting the role attribute to "force" in the trademark tag.

The code differentiates between trademarks in normal text and titles,
so if there is a trademark in a title, the symbol will be displayed
the first time in the title, and the first time in the normal text.

Basically this means that all trademarks can / should be marked up in
the documents, and the stylesheet will do "the right thing".

Looked at by: murray
Approved by: mwlucas (temp mentor)