More intelligent ordering of autocomplete search results

More intelligent ordering of autocomplete search results

Uses the php levenshtein() function.
This only works with results from the server (not autocomplete results
done via the js code).
Might change this in the future to a QuickSilver inspired sort (see,
e.g., http://github.com/rmm5t/liquidmetal) since this would result in a
sort order that is consistent if done either server-side or
browser-side.