Support for highlighting of phrase prefix queries

Prefix queries needs to be rewritten so the highlighter can work. So the pull request.

The highlight of prefix queries doesn't highlight the prefix but the full word. I have written some code on the client side to change the highlighted words. For instance, searching "ski", lucene highlight "<>skiing</>", "<>skin</>" or "<>skills</>". So my code change the highlighted parts to be: "<>ski</>in",  "<>ski</>n" or "<>ski</>lls". This code may be interesting to be on the server part, but I don't know where. If you think it is interesting, let me know.