Bug 122850 Table/list should not be able to be inserted in Master Page mode.
Description: Table/list should not be able to be inserted in Master Page mode. Steps to reproduce: 1. New a report and transfer to Master Page mode. 2. New a datasource and dataset 3. Drag a list/table to page header/footer, bind it to dataset and drag some columns inside. 4. Save and preview Expected result: Insert list/table item in master page should be forbidden. Actual result: They are allowed and preview showed "undefine" in page
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* Checks the parent element.
	 * 
	 * @param parent
	 *            the parent element
	 * @throws ExtendsException
	 *             throws <code>ExtendsException</code> if the parent element
	 *             is <code>NOT_FOUND</code>,<code>WRONG_TYPE</code>,
	 *             <code>SELF_EXTEND</code>,<code>CIRCULAR</code>.
	 */
	public void checkExtends( DesignElement parent ) throws ExtendsException
	{
		String extendsName = getExtendsName( );
		IElementDefn defn = getDefn( );
		if ( parent == null )
		{
			throw new ExtendsException( this, extendsName,
					ExtendsException.DESIGN_EXCEPTION_NOT_FOUND );
		}
		else if ( parent.getDefn( ) != defn )
		{
			throw new ExtendsException( this, parent,
					ExtendsException.DESIGN_EXCEPTION_WRONG_TYPE );
		}
		else if ( parent == this )
		{
			throw new ExtendsException( this, extendsName,
					ExtendsException.DESIGN_EXCEPTION_SELF_EXTEND );
		}
		else if ( parent.isKindOf( this ) )
		{