Add a setTimeout fallback for the transitionend listener

Webkit doesn't always reliably fire transitionend in some circumstances, which can cause the slider to stop responding.

Addresses woothemes/FlexSlider#853

Using the same closure for both `.bind("webkitTransitionEnd transitionend")` and `setTimeout()` better encapsulates the logic, and also doesn't make any assumptions about the order that they will execute in. (Though by adding an additional 200ms to the timeout, it *should* always fire after the transitionend event.  100ms seemed to give mixed results on which fired first)