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
/**
	 * base query
	 */
	private BaseQuery baseQuery;
	/**
	 * helper compiler object to fetch the pass level
	 */
	private MultiPassExpressionCompiler currentHelper;
	
	/**
	 * 
	 * @return the instance of ExpressionProcessor
	 */
	public ExpressionProcessor( DataSetRuntime dataSet )
	{
		this.dataset = dataSet;
		availableAggrList = new ArrayList( );
	}
	/**
	 * 
	 * @param computedColumns
	 * @param rsPopulator
	 * @param dataSetRuntime
	 * @throws DataException
	 */
	public void evaluateMultiPassExprOnCmp( IComputedColumnsState iccState,
			boolean useResultSetMeta ) throws DataException
	{
		assert ( iccState != null );
		Context context = Context.enter( );