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
{
		return getStringProperty( ImageItem.SIZE_PROP );
	}
	/**
	 * Returns the alternate text of this image.
	 * 
	 * @return the alternate text of the image item.
	 */
	public String getAltText( )
	{
		return getStringProperty( ImageItem.ALT_TEXT_PROP );
	}
	/**
	 * Returns the resource key of the alternate text of this image.
	 * 
	 * @return the resource key of the alternate text
	 */
	public String getAltTextKey( )
	{
		return getStringProperty( ImageItem.ALT_TEXT_KEY_PROP );
	}
	/**
	 * Returns the image source type. This is one of the following options
	 * defined in <code>DesignChoiceConstants</code>:
	 * <p>
	 * <ul>
	 * <li><code>IMAGE_REF_TYPE_NONE</code>
	 * <li><code>IMAGE_REF_TYPE_URL</code>
	 * <li><code>IMAGE_REF_TYPE_FILE</code>
	 * <li><code>IMAGE_REF_TYPE_EXPR</code>