* debian/control: added dpkg-doc

  * debian/control: added dpkg-doc
  * debian/dpkg-doc-{postinst,prerm}: new files for dpkg-doc package
  * debian/dpkg-internals: doc-base support for dpkg-doc
  * debian/rules: added build rules for dpkg-doc to binary-indep target
  * doc/Makefile.am: changed build setup for internals.sgml to use the
    debiandoc tools, and removed internals.* stuff from being built by
    default. Two new targets, internals and internals-install, now handle
    this
  * doc/changelog: removed, duplicate of ChangeLog
  * doc/internals.sgml: converted to debiandoc format, now builds correctly
    and without errors
  * doc/manuals-version: removed since it is generated at build time
  * doc/texinfo.*: moved to doc/obsolete/ since the debiandoc format doesn't
    need them
  * main/filesdb.c: fixed compiler warning