Bug 146761 All structure properties change can't be restore
Steps to reproduce: 1.New a report, extends lib.table 2.Add a structure property(such as filter, column binding...) on table 3.Choose the table, click "Restore Property" Expected result: Local propery is removed Actual result: Local property can't be removed so that "Restore Property" is always enabled
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/GroupPropertyHandle.java
* Constructs a handle to deal with an common property within a group of
	 * elements. The given property definition should be a common property
	 * shared by the collection of elements.
	 * 
	 * @param handle
	 *            Handles to a collection of elements.
	 * @param propDefn
	 *            definition of the property.
	 */
	GroupPropertyHandle( GroupElementHandle handle, ElementPropertyDefn propDefn )
	{
		assert propDefn != null;
		assert handle instanceof SimpleGroupElementHandle;
		this.handle = handle;
		this.propDefn = propDefn;
	}
	/**
	 * Indicates whether the group of element share the same value for this
	 * property.
	 * <p>
	 * If all element has a <code>null</code> value for this property, it is
	 * considered that they share the same value.
	 * 
	 * @return <code>true</code> if the group of element share the same value.
	 */
	public final boolean shareSameValue( )
	{
		Iterator iter = handle.getElements( ).iterator( );
		
		if ( !iter.hasNext( ) )