Some updates to allow ../tools/mkhowto to add various bits to the

Some updates to allow ../tools/mkhowto to add various bits to the
supplemental l2h initialization file it creates and still get all the
right behavior.  In particular, it can change the image type and icon
location and not get inconsistent results.

Some code to help suppress various navigational pages; this might be
interesting when generating HTML to create HTML Help documents, since
the navigation support creates confusing hits in the full text
search.  HTML Help also provides a lot of the navigational
infrastructure, so duplicating it makes it more tedious to use.