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/impl/ComputedColumnHelper.java
/*
	 * @see org.eclipse.birt.data.engine.odi.IResultObjectEvent#process(org.eclipse.birt.data.engine.odi.IResultObject)
	 */
	public boolean process( IResultObject resultObject, int rowIndex )
			throws DataException
	{
		logger.entering( ComputedColumnHelper.class.getName( ), "process" );
		assert resultObject != null;
		IResultClass resultClass = resultObject.getResultClass( );
		if ( isPrepared == false )
			prepare( resultClass );
		
		
		if ( computedColumn.length == 0 )
		{
			logger.exiting( ComputedColumnHelper.class.getName( ), "process" );
			return true; 
		}
		
		dataSet.setRowObject( resultObject, true );
		dataSet.setCurrentRowIndex( rowIndex );
		
		
		Context cx = Context.enter( );
		try
		{
			
			
			for ( int i = 0; i < computedColumn.length; i++ )
			{