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 ExprManager exprManager;
	
	/**
	 * No external instance
	 */
	private ExprManagerUtil( )
	{
	}
	
	/**
	 *	This method tests whether column bindings in ExprManager is valid or not.
	 * 
	 * @param exprManager
	 * @return
	 * @throws DataException
	 */
	public static void validateColumnBinding( ExprManager exprManager )
			throws DataException
	{
		ExprManagerUtil util = new ExprManagerUtil( );
		
		util.exprManager = exprManager;
		util.checkDependencyCycle( ); 
		util.checkGroupNameValidation( );
	}
	/**