currentSlide should be set in the same place for all animation types

Problem/Motivation:

slider.currentItem can return different results depending on whether or not css animations are enabled.  This is because `slider.currentSlide = slider.animatingTo;` can either happen in `slider.flexAnimate()` or in `slider.wrapup()`

This was causing us issues using `slider.canAdvance()` (we are using https://github.com/markirby/FlexSlider-ManualDirectionControls which relies on this method).

Proposed Solutions:
`slider.currentSlide = slider.animatingTo;` should happen in the same place for all animations, regardless of their type.