ScaleManager Fullscreen Mode does not "start/enter" in IE11; triggers MSFullscreenError event

[pnstickne]

I've added Fullscreen Error support (and the appropriate prefixed Fullscreen API support) for IE in #1278 - however, FS support in IE11 still does not work; and it doesn't work in master either or any of the 2x branches I've seen either; the MSFullscreenError event is always called.

Fullscreen in IE11 does work when startFullScreen is invoked from a "simple click handler". This may indicate that the issue is related to the depth/handling of the input system.

[pnstickne]

Specifically (in IE11, desktop), changing to Fullscreen does not work with "MSPointerDown" events, but it does work with "click" events.

[pnstickne]

Should be addressed with the merges.