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/executor/aggregation/AggregationHelper.java
if ( (!isRunning) && populateValue )
			{
				Object value = acc.getValue( );
				currentRoundAggrValue[aggrIndex].add( value );
			}
		}
		return true;
	}
	
	/**
	 * Prepare next run of aggregation pass.
	 * 
	 * @param validAggregations
	 * @param populateAggrValue
	 * @param count
	 * @throws DataException 
	 */
	private void prepareNextIteration( List validAggregations,
			boolean[] populateAggrValue, int count ) throws DataException
	{
		validAggregations.clear( );
		for ( int i = 0; i < this.currentAggrCount; i++ )
		{
			this.accumulatorManagers[i].restart( );
			IAggregation temp = this.getAggrInfo( i ).getAggregation( );
			populateAggrValue[i] = false;
			if ( temp instanceof Aggregation )
			{
				int passesNumber = ( (Aggregation) temp ).getNumberOfPasses( );