Event listeners are not freed

[mjeffrie]

Event listeners are created and sometimes not removed. This leads to memory leaks.

This happens when isCaptureMode is true, since removeEventListener needs the same useCapture flag as used in addEventListener.

Possible fixes include:

1. calling removeEventListener twice with true and false for useCapture.
2. storing the useCapture value used by addEventListener and using it when calling removeEventListener.
3. providing currentTarget to determine isCaptureMode when calling removeEventListener.