Bug 177504 Engine doesn't provide SubQuery for extended item
Engine doesn't provide SubQuery for extended item, so chart can't use container's binding to execute the query. If possible, engine could provide an option for extended item to choose whether engine could create the query, so extended item won't create SubQuery by itself.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/extension/internal/RowSet.java
this( context, rset, false );
	}
	public RowSet( ExecutionContext context, IQueryResultSet rset,
			boolean isOutterResultSet )
	{
		this.context = context;
		this.isOutterResultSet = isOutterResultSet;
		closed = false;
		this.rset = rset;
		metaData = new IRowMetaData( ) {
			public int getColumnCount( )
			{
				return 0;
			}
			public String getColumnName( int index ) throws BirtException
			{
				return null;
			}
			public int getColumnType( int index ) throws BirtException
			{
				return -1;
			}
		};
		if ( rset != null )
		{
			try
			{
				metaData = new RowMetaData( rset.getResultMetaData( ) );
			}
			catch ( BirtException ex )