Bug 137917 ImageHandle add setFile method.
According to new Resource Deployment Specification, image builder add a new image type 'File', so ImageHandle should add 'setFile' method as other type methods such as 'setURI'.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/ImageHandle.java
* <li>image presented by URL
 * <li>expression which returns the image contents
 * </ul>
 * <p>
 * The image has the following properties:
 * <ul>
 * <li>An optional hyperlink for this image.
 * <li>An optional help text for the image.
 * <li>An optional text message to display in place of the image in a web
 * browser.
 * </ul>
 * 
 * The image item can be sized to the image (in which case the height and width
 * attributes are ignored), or the image can be sized or clipped to fit the
 * item. Images are always scaled as percentage proportionately.
 * 
 * 
 * @see org.eclipse.birt.report.model.elements.ImageItem
 * @see org.eclipse.birt.report.model.api.elements.DesignChoiceConstants
 */
public class ImageHandle extends ReportItemHandle implements IImageItemModel
{
	/**
	 * Constructs a image handle with the given design and the element. The
	 * application generally does not create handles directly. Instead, it uses
	 * one of the navigation methods available on other element handles.
	 * 
	 * @param module
	 *            the module
	 * @param element