suggestion for adding a l10n-capable doc-format navi

[Hiroki Sato]

Hi,

 I have committed the patch.  All of docs in {en_US.ISO8859-1,
 ja_JP.eucJP}/articles/ and {en_US.ISO8859-1,ja_JP.eucJP}/books/ now
 have a link that can be used for readers to choose split and single
 HTML version.

 For translation teams, please do the following:
  
  a) add PUBLIC "-//FreeBSD//ENTITIES DocBook Language Specific Entities//EN"
     to <langcode>/share/sgml/catalog (use "//EN" for all languages,
     not other language code like "//JA").  This entity set is
     for l10n purpose, and is used for WITH_DOCFORMAT_NAVI_LINK feature
     now.  The substance is a file <langcode>/share/sgml/l10n.ent.
     See en_US.ISO8859-1/share/sgml/l10n.ent for example.
  
     Note that when the entity set is not defined, the default
     one (share/sgml/l10n.ent) is used.

  b) add WITH_DOCFORMAT_NAVI_LINK?=YES to Makefile as done for
     en_US.ISO8859-1/ directory.

 Although it should not break the doc/ build, I could miss
 something.  If anyone notice building (or rendering) failure,
 please let me know.

-- 
| Hiroki SATO  <hrs at eos.ocn.ne.jp> / <hrs at FreeBSD.org>