Properly check for async events related to capture

http://www.w3.org/2012/pointerevents/track/actions/126
Because this test already had explicit checks for each event, I just used the existing code, rather than matching the assertion in for the `gotpointercapture` test.

This test was actually written incorrectly the first time because it was setting all the flags in `gotpointercapture`, but by design there had to be events occurring between `gotpointercapture` and `lostpointercapture`. I simplified the test by just releasing the capture after setting the capture. This ensures that the flags are representing the correct state.