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
setProperty( ImageItem.SOURCE_PROP, source );
	}
	/**
	 * Returns the image URI if the image source type is
	 * <code>IMAGE_REF_TYPE_URL</code> or <code>IMAGE_REF_TYPE_FILE</code>.
	 * 
	 * @return the image URI if the image source type is
	 *         <code>IMAGE_REF_TYPE_URL</code> or
	 *         <code>IMAGE_REF_TYPE_FILE</code>. Otherwise, return
	 *         <code>null</code>.
	 */
	public String getURI( )
	{
		if ( DesignChoiceConstants.IMAGE_REF_TYPE_URL
				.equalsIgnoreCase( getSource( ) )
				|| DesignChoiceConstants.IMAGE_REF_TYPE_FILE
						.equalsIgnoreCase( getSource( ) ) )
		{
			return getStringProperty( ImageItem.URI_PROP );
		}
		return null;
	}
	/**
	 * Returns the type expression of the image item if the image source type is
	 * <code>IMAGE_REF_TYPE_EXPR</code>.
	 * 
	 * @return the type expression, if the image source type is
	 *         <code>IMAGE_REF_TYPE_EXPR</code>. Otherwise, return
	 *         <code>null</code>.
	 *