Make controlled components and bubbling work in IE

Fixes #708.

Test Plan:
In IE9, tested a controlled text input with the event handler on a containing element, as in the fiddle linked in the original issue. Also tested a controlled radio button as the logic there differs within ReactDOMInput. In both cases, I was able to interact with the controls.

The IE events aren't currently covered by unit tests and it's not easy to add them, but I'm comfortable merging this without automated tests; this merely brings the batching behavior here in line with our other event handling.