Log Message:
Update to 2.6.0:

 * catalog, catalog.xml: enable users to have "current" in schema URIs
   in doc instances;

   http://docbook.sourceforge.net/release/website/current/schema/

   Yeah, I know that it's traditionally been the case that DocBook
   doc instances contain public and system IDs for a specific version
   of the DocBook DTD. But note that:

     - all versions of DocBook 4 are backward-compatible

     - doc instances don't actually need to contain any system or
       public ID at all users employ RELAX NG-based tools

     - for RELAX NG-based toolchain, users will probably be authoring
       and validating their doc instances against whatever is the
       current version of the RELAX NG schema for DocBook that that
       they have installed

   So enabling users to put "current" in their doc instances instead
   of a specific version number means that they don't need to update
   the URIs if/when they want to author/validate using a future
   version of the DTD.

 * AUTHORS, BUGS, COPYING, INSTALL, README, TODO: Added standard distro
   files, to make life easier for packagers;

   From README, moved copyright info to COPYING and install info to
   INSTALL. README content is not just minimal how-to info. Added
   BUGS and TODO, which are just pointers to SF trackers. Added
   AUTHORS just for sake completeness.

 * Makefile: generate RELEASE-NOTES.html/.txt

 * RELEASE-NOTES.xml: New file.