Make a special case for pointerdown, since it's a weird new feature from IE11. It's part of the event chain (pointerdown, pointerup, mousedown, etc.) so when you call preventDefault on it, it stops mousedown from being called. However it's not a 'touch' event so it doesn't fit into existing support for touch.
Build files.
Merge pull request #44 from code-dot-org/ie11fix

Ie11fix