I get some improvements here in performance (for non-prox queries) by hacking up luceneutil to
test queries with postingshighlighter+offsets vs fastvectorhighlighter+vectors.
However, I don't think this will be realistically useful until we have the new block layout from the pfor branch:
prox queries are hurt by the interleaving in the stream (just like if you use payloads), unrelated to highlighting.
I tried to do more experiments like 'wikibig' in luceneutil but i ran out of disk space.
Once we have the block layout landed lets revisit this: it gives a much smaller index, faster indexing,
and I think will work well when thats sorted out.