Fix for file access issues on search

[lhagan]

This fix solves the issues I reported in issue #10 (read past EOF and Too many open files errors on after multiple searches).

[lhagan]

I'm going to leave this request open in case it helps someone else track down the actual problem, but this is definitely not the right way to fix this problem. IndexReader* get_reader looks like it's intended to re-use the same instance instead of opening a new one each time, but it doesn't.