8u40 review request: RT-38923 OOM on animating transparent windows

[Jim Graham]

webrev: http://cr.openjdk.java.net/~flar/RT-38923/webrev.00/
Jira: https://javafx-jira.kenai.com/browse/RT-38923

The main issues are testing this in various configurations and with whatever tests were used that led us to the previous solution of having an unbounded number of outstanding pixel buffers in flight in the upload queue.  I mainly tested with the test case in the description of the Jira issue on Mac (which doesn't use the UploadingPainter) and Win 7 (where I could reproduce the problem)...

		...jim