Mystery at least partially solved: it appears that in the FreeBSD
catalog we must list the iso8859 catalog *before* the docbook catalog,
otherwise things don't work properly.
+CATALOG /usr/local/share/sgml/iso8879/catalog
CATALOG /usr/local/share/sgml/docbook/catalog
CATALOG /usr/local/share/sgml/docbook/dsssl/modular/catalog
-CATALOG /usr/local/share/sgml/iso8879/catalog
CATALOG /usr/local/share/sgml/jade/catalog