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
List bindingExprs = exprManager.getBindingExprs( );
		HashMap l = new HashMap( );
		for ( int i = 0; i < bindingExprs.size( ); i++ )
		{
			String key = ( (GroupBindingColumn) bindingExprs.get( i ) ).getGroupKey( );
			Integer groupLevel = new Integer( ( (GroupBindingColumn) bindingExprs.get( i ) ).getGroupLevel( ) );
			if ( key != null )
				l.put( groupLevel, key );
		}
		return l;
	}
	
	/**
	 *
	 */
	static class Node
	{
		private List children;
		private String value;
		/**
		 * @param value
		 */
		Node( String value )
		{
			this.value = value;
			this.children = new ArrayList( );
		}
		/**
		 * @return
		 */