Docbook requires sections to have titles, but if they're empty it writes
out a '???' title, having not title seems cleaner. Can be fooled by
putting empty phrase markup in the title, so might need to be a little
smarter about that.
I'm considering adding a warning, perhaps an error in strict mode.
This encapsulates more in the id and section handling code. Fixes a few
edge cases and separates implementation of the new and old section
handling code. Always normalizes and truncates generated ids in quickbook
1.6.
[SVN r75251]