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
{
			if ( nodes[i].equals( node ) )
				return nodes[i];
		}
		return null;
	}
	
	/**
	 * 
	 * @return
	 */
	private List getColumnNames( )
	{
		List bindingExprs = exprManager.getBindingExprs( );
		Map autoBindingExprMap = exprManager.getAutoBindingExprMap( );
		List l = new ArrayList( );
		l.addAll( autoBindingExprMap.keySet( ) );
		for ( int i = 0; i < bindingExprs.size( ); i++ )
		{
			l.addAll( ( (GroupBindingColumn) bindingExprs.get( i ) ).getColumnNames( ) );
		}
		return l;
	}
	
	/**
	 * 
	 * @return
	 */
	private HashMap getGroupKeys( )
	{