Lucene:AccessProxy::AccessProxy(): control hits.data access

We should probably extend this class to support flags that can in turn control open() and access semantics of hits.data, just like we should do (via an aux.function or a wrapper) for the actual index data. See [here](http://blog.mikemccandless.com/2010/06/lucene-and-fadvisemadvise.html?m=1) for rationale.