Fixed bug: first_indexed value in change_tracker updated inappropriately.
Resolves VUFIND-835; thanks to Luke O'Sullivan for the fix.
Added missing @link tags to satisfy coding standards.
Added comments.
New recommendation module: SummonResultsDeferred.
Resolves VUFIND-838.
Created handler-related lookup methods to simplify SearchTabs helper.
Made SearchObject recommendations smarter about search handlers.
Made SearchObject recommendations smarter about advanced searches.