LayoutTest for WebCL<->WebGL Interoperability

        Issue #42
        Create the LayoutTest and add interoperability functions to
        WCLCommandQueue.

        Reviewed by Afonso Costa.

        * webcl/resources/webcl-proxy.js:
        * webcl/tests/webcl-test-interop-expected.txt: Added.
        * webcl/tests/webcl-test-interop.html: Added.