Implement tests for WebCLEvent

issue #50

        Reviewed by NOBODY (OOPS!).

        * webcl/resources/webcl-proxy.js:
         Change webc-proxy to allow user set device type in
         WCLPlatform::getWCLDevice.

        * webcl/tests/webcl-test-event.html:
         Change callback function in webcl-test-event to
         increment a global var that cab be validated to
         pass ou fail the test.

         Added instanceof test for WebCLEvent objects.

        * webcl/tests/webcl-test-event-expected.txt: