#71: add lucene backward codecs as optional dependency
#71: add lucene backward codecs as optional dependency

Backwards codecs can be used to read indices created with an older
lucene version

Signed-off-by: Andreas Schwarte <e77d70c35db7acb5c1ca19e621121dcbb9bab6a2@gmail.com>
eclipse/rdf4j,eclipse/rdf4j,eclipse/rdf4j,eclipse/rdf4j,eclipse/rdf4j,eclipse/rdf4j