Reduce calls to GQuery.children for performance

On a long list (e.g. 5000 items) the calls to GQuery.children would add as much as 2 seconds to the time spent in ChosenListbox.onLoad
Improve performance of winnowResultsSetHighlight

The version that used GQuery.find was a fairly big performance hit on long lists
Make search term highlighting optional

If the list is long, and the first few type characters match a lot of items (as it often the case) then the calls to GQuery.html would have a significant performance impact.
Make the highlighting optional (default: on) so that in use cases with long lists it can be turned off for performance reasons.
Merge pull request #89 from tvernum/long-list-performance

Performance improvements for long lists