WebCL Conformance test suite update.

    Summary ::

    Add functionality testcases for enqueueCopyBufferRect.
    Correcting comparison of descriptor objects in cl_context_getSupportedImageFormats.html
    Modify test case verifying exception INVALID_IMAGE_SIZE in createImage files across testsuite.
    Calling testcases only on loading on video in HTMLInterop.
    Making enqueue{Read, Write} operations calls as unblocking being waited on userevents.
    Misc spelling corrections in resources/js-test-pre.js

    Contributors :
    SRI-B : Shilpa Shri, Sharath Kamath.
    SRA : Antonio Gomes and Steven Eliuk.