Add Japanese 5.0-RELEASE release docs and activate them:

1.54 -> 1.55 includes.sgml
1.11 -> 1.12 includes.xsl
1.43 -> 1.46 index.xsl
1.83 -> 1.85 releases/index.sgml
1.14 -> 1.16 releases/snapshots.sgml
(new) -> 1.6 releases/5.0R/Makefile
(new) -> 1.1 releases/5.0R/Makefile.inc
(new) -> 1.3 releases/5.0R/announce.sgml
(new) -> 1.1 releases/5.0R/docbook.css
(new) -> 1.3 releases/5.0R/hardware.sgml
(new) -> 1.3 releases/5.0R/installation.sgml
(new) -> 1.2 releases/5.0R/relnotes.sgml