Add new textChange event: input + IE shim

IE8 doesn't support oninput and IE9 supports it badly but we can do
almost a perfect shim by listening to a handful of different events
(focus, blur, propertychange, selectionchange, keyup, keydown).

This always triggers event handlers during the browser's event loop (not
later in a setTimeout) and after the value property has been updated.

The only case I know of where this doesn't fire the event immediately is
if (in IE8) you modify the input value using JS and then the user does a
key repeat, in which case we fire the event on the second keydown.

Test Plan:
Modify ballmer-peak example to add es5-shim and to use onTextChange
instead of onInput. In IE8, IE9, and latest Chrome, make sure that the
event is fired upon:

* typing normally,
* backspacing,
* forward-deleting,
* cutting,
* pasting,
* context-menu deleting,
* dragging text to reorder characters.

After modifying the example to change .value, make sure that the event
is not fired as a result of the changes from JS (even when the input box
is focused).