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
* compile the expression from a script tree
	 * 
	 * @param expression
	 * @param context
	 * @param tree
	 * @param columnExprList
	 * @throws BirtException
	 */
	private void CompiledExprFromTree( String expression, Context context,
			ScriptOrFnNode tree, List columnExprList ) throws BirtException
	{
		if ( tree.getFirstChild( ) == tree.getLastChild( ) )
		{
			if ( tree.getFirstChild( ).getType( ) == Token.FUNCTION )
			{
				int index = getFunctionIndex( tree.getFirstChild( ).getString( ),
						tree );
				compileFunctionNode( tree.getFunctionNode( index ),
						tree,
						columnExprList );
			}
			else
			{
				
				if ( tree.getFirstChild( ).getType( ) != Token.EXPR_RESULT
						&& tree.getFirstChild( ).getType( ) != Token.EXPR_VOID
						&& tree.getFirstChild( ).getType( ) != Token.BLOCK )
				{
					
					throw new CoreException( pluginId,