(bug 35119) show poll results only for users who voted (options to override)

0. bump version 1.81 20130526

1. new: poll results are by default _not_ shown when the user has not voted

2. a new optional (per-poll) tag parameter "show-results-before-voting" is introduced
   <poll show-results-before-voting>
   <poll show-results-before-voting=1>

3. introduction of new group permissions:

   * ajaxpoll-viewresults
   * ajaxpoll-viewresults-before-voting

4. schema change
   this version requires a database update ( php maintenance/update.php )
   updater included

Change-Id: Iae1f3f2806afecbca3e3c41460dbbf20fc557525