Bug 61713 MessageDialog can't be created in non UI thread anymore
I20040511 In the past it was possible to create a MessageDialog from non UI threads. This is not possible with I20040511 anymore. Doing so now results in an invalid thread access to due the fact that the images are now managed by SWT.
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ImageRegistry.java
if (entry == null) {
			return null;
		}
		if (entry.image == null && entry.descriptor != null) {
			entry.image = entry.descriptor.createImage();
		}
		return entry.image;
	}
	/**
	 * Returns the descriptor associated with the given key in this registry, 
	 * or <code>null</code> if none.
	 *
	 * @param key the key
	 * @return the descriptor, or <code>null</code> if none
	 * @since 2.1
	 */
	public ImageDescriptor getDescriptor(String key) {
		Entry entry = getEntry(key);
		if (entry == null) {
			return null;
		}
		return entry.descriptor;
	}
	/**
	 * Shut downs this resource registry and disposes of all registered images.
	 */
	void handleDisplayDispose() {
		
		if (table == null)
			return;