Bug 148951 Wrong error msg when set nonexisted col as group key
Description: Wrong error msg when set nonexisted col as group key Steps to reproduce: 1. Insert a table, bind it to dataset 2. Add a group, input abc as group key which is invalid. 3. Preview Expected result: Friendly error msg to tell user the group key is wrong. Actual result: + Group key "abc" in group 1 cannot depend on column bindings defined in the group lower than itself. data.engine.InvalidGroupKey ( 1 time(s) ) detail : org.eclipse.birt.data.engine.core.DataException: Group key "OUNTR" in group 1 cannot depend on column bindings defined in the group lower than itself.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/ExprManagerUtil.java
*/
	private Node[] populateNodeList( Node[] source )
	{
		Node[] result = new Node[source.length];
		for ( int i = 0; i < result.length; i++ )
		{
			result[i] = new Node( source[i].getValue( ) );
		}
		for ( int i = 0; i < result.length; i++ )
		{
			List l = source[i].getChildren( );
			for ( int j = 0; j < l.size( ); j++ )
			{
				Node n = getMatchedNode( (Node) l.get( j ), result );
				
				if( n!= null )
					result[i].addChild( n );
			}
		}
		return result;
	}
	/**
	 * 
	 * @param node
	 * @param nodes
	 * @return
	 */
	private Node getMatchedNode( Node node, Node[] nodes )
	{
		for ( int i = 0; i < nodes.length; i++ )