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
if ( baseExpression instanceof IScriptExpression )
					{
						exprInfo = new ExpressionInfo( (IScriptExpression) baseExpression,
								exprType,
								currentGroupLevel,
								useResultSetMeta );
						baseExpression.setHandle( helper.compileExpression( exprInfo,
								context ) );
					}
					else if ( baseExpression instanceof IConditionalExpression )
					{
						compileConditionalExpression( (IConditionalExpression) baseExpression,
								helper,
								rsPopulator,
								exprType,
								currentGroupLevel,
								context );
					}
					
					
					if ( exprType == GROUP_COLUMN_EXPR )
					{
						return;
					}
					
					
					if ( helper.getExpressionPassLevel( ) <= 1 )
					{
						iccState.setValueAvailable( i );
					}