Bug 150593 Enhancements for ResourceManager
The attached patch addresses the following in ResourceManager - Fixes several JavaDoc bugs - Adds a "getImage" method that implements the common pattern of "return existing image if known, or allocate a new image otherwise"
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ResourceManager.java
*
     * @param descriptor identifier for the resource
     */
    public abstract void destroy(DeviceResourceDescriptor descriptor);
    
    /**
     * Creates an image, given an image descriptor. Images allocated in this manner must
     * be disposed by {@link #destroyImage(ImageDescriptor)}, and never by calling 
     * {@link Image#dispose()}.
     * 
     * @since 3.1 
     *
     * @param descriptor descriptor for the image to create
     * @return the Image described by this descriptor (possibly shared by other equivalent
     * ImageDescriptors)
     * @throws DeviceResourceException if unable to allocate the Image
     */
    public final Image createImage(ImageDescriptor descriptor) throws DeviceResourceException {
    	
    	Assert.isNotNull(descriptor);
    	
        return (Image)create(descriptor);
    }
    
    /**
     * Creates an image, given an image descriptor. Images allocated in this manner must
     * be disposed by {@link #destroyImage(ImageDescriptor)}, and never by calling 
     * {@link Image#dispose()}.
     * 
     * @since 3.1