Fixed issue where intro:pageAppeared:withIndex: delegate method wasn't being called with tapToNext enabled.

The _currentPageIndex was being set in setCurrentPageIndex:animated so by the time checkIndexForScrollView: was called after the scroll in scrollViewDidEndScrollingAnimation:, notifyDelegateWIthPreviousPage:andCurrentPage had no side effect because the previousPage and currentPage indexes were equal at that point.

Resolves #53