Use WebKit memory allocation functions instead of malloc
        Issue #50

        Reviewed by Antonio.

        In WebKit is not recommend to use malloc directly, because WTF
        implements an optimized memory allocator.
        This patch just changes the WebCLCommandQueue, other classes will be
        changed in the future.

        * Modules/webcl/WebCLCommandQueue.cpp:
        (WebCore::WebCLCommandQueue::enqueueWriteBufferRect):
        (WebCore::WebCLCommandQueue::enqueueReadImage):
        (WebCore::WebCLCommandQueue::enqueueReadBufferRect):
        (WebCore::WebCLCommandQueue::enqueueNDRangeKernel):
        (WebCore::WebCLCommandQueue::enqueueWriteImage):
        (WebCore::WebCLCommandQueue::enqueueCopyImage):
        (WebCore::WebCLCommandQueue::enqueueCopyImageToBuffer):
        (WebCore::WebCLCommandQueue::enqueueCopyBufferToImage):
        (WebCore::WebCLCommandQueue::enqueueCopyBufferRect):