Commit a97e85f2 caused "exceed the available area" warnings in PDF
builds.  Fine-tune colwidth values to avoid that.

Back-patch to 9.6, like the prior patch.  (This is of dubious value
before v13, since we were far from free of such warnings in older
branches.  But we might as well keep the SGML looking the same in all
branches.)

Per buildfarm.