bcd0d8fe9b
There were two problems: 1) When starting the mimic, we put up a bad frame because although we set the `begin` value of the animation, we were building using the current `value`, which hadn't been updated. 2) When stoping the mimic, we'd dirty a component during didUnmount, which wouldn't get cleaned until the next frame. Now we're sure to clean all the components before leaving flushBuild.