Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ExtendsCommand.java
ActivityStack activityStack = getActivityStack( );
		activityStack.startTrans( );
		try
		{
			if ( parent.getDefn( ).allowsUserProperties( ) )
			{
				Iterator iter = parent.getUserProperties( ).iterator( );
				while ( iter.hasNext( ) )
				{
					UserPropertyDefn userPropDefn = (UserPropertyDefn) iter
							.next( );
					UserPropertyCommand command = new UserPropertyCommand(
							module, element );
					command.addUserProperty( userPropDefn );
				}
			}
			
			Iterator iter = parent.getDefn( ).getProperties( ).iterator( );
			while ( iter.hasNext( ) )
			{
				ElementPropertyDefn propDefn = (ElementPropertyDefn) iter
						.next( );
				String propName = propDefn.getName( );
				if ( !propDefn.canInherit( ) )
					continue;
				
				
				
				if ( StyledElement.STYLE_PROP.equals( propName )
						|| DesignElement.EXTENDS_PROP.equals( propName )