Doc: marginal hacking to remove some PDF build warnings.

Doc: marginal hacking to remove some PDF build warnings.

This patch eliminates a few more "exceed the available area" warnings
whose causes aren't particularly connected to anything else.

The only one really worthy of comment is that I increased the space
allowed for an <orderedlist>'s numbers, because the default of 1em
doesn't quite work for more than one digit.  The rest are one-off
insertions of &zwsp; and suchlike tweaks, in places where they
shouldn't do any damage to the material.  (In particular, although
I split some long identifiers with zwsp's, there are other nearby
occurrences of each one; so those changes shouldn't hurt greppability
of the document sources.)