Bug 189706 Enhance computed column aggregation function handling in UI.
Due to the issue discussed in 189705, current computed column aggregation builder in data set editor has bugs to extend: 1.When new a computed column, the aggregation argument field cannot be correctly set. 2.The argument field cannot be correct grayed out when user select a aggregation function without arguments 3.The available aggregation function list is incomprehensive 4.Some aggregation function cannot be set to model(say, weightedAve).
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/expression/ExpressionProcessor.java
{
	IScriptExpression scriptExpr;
	int exprType;
	int currentGroupLevel;
	boolean customerChecked = false;
	/**
	 * 
	 * @param scriptExpression
	 * @param exprType
	 * @param currentGroupLevel
	 * @param useCustomerChecked
	 */
	ExpressionInfo( IScriptExpression scriptExpression, int exprType,
			int currentGroupLevel, boolean useCustomerChecked )
	{
		this.scriptExpr = scriptExpression;
		this.exprType = exprType;
		this.currentGroupLevel = currentGroupLevel;
		this.customerChecked = useCustomerChecked;
	}
	/**
	 * 
	 * @return