Added refresh timer that prevents refreshing content too often.
Removed isPlayBackRateSupported() - defunct.
Logging in stack renderer.
More aggressive preloading in stack renderer.
Removed FIXME.
Fixed tiny bug introduced in commit 4f7024e5ec8f2d591203e72b2dd3216574d63bb2.
Fixed recursion bug in stack renderer.
Fixed issue #467: TextWindow is hiding text on iphone (IOS6).