* New configure options, texdir and perllibdir, so this addresses are set at
  the configuration stage. Modified debian/rules and Makefile.in to use them.
* No longer substitute bin/linuxdoc.in from configure. Variables like
  ${pkgdatadir} were replaced unexpended this way. Better replace from
  Makefile as before, so everything (e.g., things like
  ${datadir}/linuxdoc-tools) is replaced fully expanded, as suggested in the
  'Installation Directory Variables' section of the autoconf manual.
* Other changes in Makefile.in:
  - Explicitly pass perl5libdir to entities Makefile.
  - Pass $(prefix) prefixed with $(DESTDIR) when buildong docs.
* bin/linuxdoc.in: Make sure we always look in @pkgdatadir@ and @perl5libdir@