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
IScriptExpression op = condition.getExpression( );
				IScriptExpression op1 = condition.getOperand1( );
				IScriptExpression op2 = condition.getOperand2( );
				if ( op != null )
					helper.compileExpression( op, context );
				if ( op1 != null )
					helper.compileExpression( op1, context );
				if ( op2 != null )
					helper.compileExpression( op2, context );
			}
			else if ( baseExpression instanceof IScriptExpression )
			{
				IScriptExpression scriptExpr = (IScriptExpression) baseExpression;
				helper.compileExpression( scriptExpr, context );
			}
		}
		finally
		{
			Context.exit( );
		}
	}
	
	/**
	 * Return the index of group according to the given group text.
	 * @param groupText
	 * @return The index of group 
	 */
	private int getCurrentGroupLevel( String groupText, int start, BaseQuery query )
	{
		assert groupText != null;