iOS 6 bugfix

Some older browsers had vendor specific prefixes before the javascript requestAnimationFrame and cancelAnimationFrame functions. Previously only the requestAnimationFrame prefix were being checked for. As a result, it used the vendor prefix for requestAnimationFrame, but did not use it for cancelAnimationFrame.

Additionally, TimeCircles only checked if requestAnimationFrame was available- it did not check if cancelAnimationFrame was also available.

These problems has been fixed.