Bug 130492 Provide a method to serialize the report with library information.
Currently, when engine generate the report document file, the document does not contain any library information. That will cause many propblem on server side. Model should provide a method to serialize the report with library information to a stream so that the generated report document can contain all information that the report need.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/elements/JointDataSet.java
{
		return ReportDesignConstants.JOINT_DATA_SET;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.api.core.IDesignElement#getHandle(org.eclipse.birt.report.model.core.Module)
	 */
	public DesignElementHandle getHandle( Module module )
	{
		return handle( module );
	}
	/**
	 * Returns an API handle for this element.
	 * 
	 * @param module
	 *            the report design of the joint data set
	 * 
	 * @return an API handle for this element
	 */
	public JointDataSetHandle handle( Module module )
	{
		if ( handle == null )
		{
			handle = new JointDataSetHandle( module, this );
		}
		return (JointDataSetHandle) handle;
	}
}