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
* multiple pass level Each expression is compiled to generate a handle, which
 * is an instance of CompiledExpression or its derived class. The expression
 * handle is used by the factory to evaluate the expression after the report
 * query is executed. <br>
 * ExpressionProcessor compiles the expression into Rhino byte code for faster
 * evaluation at runtime.
 *  
 */
public class ExpressionProcessor implements IExpressionProcessor
{
	/**
	 * the available aggregate list in expression processor
	 */
	private List availableAggrList;
	/**
	 * data set runtime
	 */
	private DataSetRuntime dataset;
	/**
	 * result set populator
	 */
	private ResultSetPopulator rsPopulator;
	/**
	 * is dataset mode or result set mode
	 */
	private boolean isDataSetMode = true;
	/**
	 * resultset iterator
	 */
	private IResultIterator resultIterator;