Non-Free SGML entity files

[stressware@cock.li]

The package sgml-data includes non-Free files in the
'sgml/entities/sgml-iso-entities*/' directories and the
'sgml/html/entities/' directory under the following licence:

  'Permission to copy in any form is granted for use with conforming
   SGML systems and applications as defined in ISO 8879, provided this
   notice is included in all copies.'

And files based on files with that licence are in
'xml/entities/xml-iso-entities-8879.1986' in the same source package.

Unless 'conforming SGML systems and applications' is broadly defined
in ISO 8879, then redistribution is highly restricted (I cannot check
ISO 8879, because it seems there is no gratis copy).

Files under the same licence are also included in linuxdoc-tools in
the directories 'iso-entities/entities/' and 'entity-map/sdata/' (for
example ISOtech).

Furthermore, files in the directory
'classpath/tools/resource/gnu/classpath/tools/gjdoc/dtd/ent/' in GCC
are based on these files.

The SGML entity files are needed to build documentation for several
projects, I believe.

It seems like it would be difficult to write the SGML entity files
much differently, so it is possible that they are not copyrightable.

Also, I believe that files under the offending licence, or derivative
files are included in other packages, though they might not be
installed.