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
if ( computedColumn[i].getExpression( ) != null )
				{
					Object value = null;
					try
					{
						if ( computedColumn[i].getExpression( ).getHandle( ) != null )
							value = ( (CompiledExpression) computedColumn[i].getExpression( )
									.getHandle( ) ).evaluate( cx,
									dataSet.getScriptScope( ) );
						else
						{
							value = ScriptEvalUtil.evaluateJSAsExpr( cx,
									dataSet.getJSDataSetObject( ),
									( (IScriptExpression) computedColumn[i].getExpression( ) ).getText( ),
									"ComputedColumn",
									0 );
						}
						if ( computedColumn[i] instanceof GroupComputedColumn )
						{
							try
							{
								value = ( (GroupComputedColumn) computedColumn[i] ).calculate( value );
							}
							catch ( BirtException e )
							{
								throw DataException.wrap( e );
							}
						}
						value = DataTypeUtil.convert( value,
								resultClass.getFieldValueClass( columnIndexArray[i] ) );