Bug 145022 Provide a utility method to help GUI enhance aggregate on.
DtE will provide a method hasAggregation(String expression) in org.eclipse.birt.core.data.ExpressionUtil, and the return value will be true when the expression is a valid JS expression and it has aggregation defined.
core/org.eclipse.birt.core/src/org/eclipse/birt/core/data/ExpressionParserUtility.java
* 
	 * @param context
	 * @param parent
	 * @param callNode
	 * @throws BirtException
	 */
	private void compileAggregateExpr( Node parent, Node callNode,
			ScriptOrFnNode tree, List columnExprList ) throws BirtException
	{
		assert ( callNode.getType( ) == Token.CALL );
		compileAggregationFunction( callNode, tree, columnExprList );
		extractArguments( callNode, tree, columnExprList );
	}
	/**
	 * 
	 * @param callNode
	 * @param tree
	 * @param columnExprList
	 * @throws BirtException
	 */
	private void compileAggregationFunction( Node callNode,
			ScriptOrFnNode tree, List columnExprList ) throws BirtException
	{
		Node firstChild = callNode.getFirstChild( );
		compileComplexExpr( firstChild, tree, columnExprList );
	}
	/**
	 * extract arguments from aggregation expression
	 * 
	 * @param context