Common SGML utils

The sgml-common package gathers very basic stuff necessary to work with SGML and XML, such as xml.dcl, a SGML declaration of XML; iso-entities, a list of the basic SGML ISO entities; and install-catalog, a script used to add entries to (or remove entries from) centralized catalogs whose entries are pointers to SGML open catalogs, as defined by OASIS. It also includes sgmlwhich, a small script which prints where the SGML main configuration file is located (provided for compatibility with non-FHS systems).