Bug 141959 Changing data set didn't clean old column bindings
Steps to reproduce: 1.Add two data sets, "ds1" and "ds2" 2.Add a table, binding with "ds1". All "ds1" column bindings generate automatically, that's good 3.Change "ds1" to None Expected result: All "ds1" column bindings should be cleaned Actual result: All "ds1" column bindings are still there. If changing to "ds2", "ds2" column bindings will be added after them.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ColumnBindingDialog.java
text = ChoiceSetFactory.getDisplayNameFromChoiceSet( handle.getDataType( ),
							dataTypeChoiceSet );
					break;
				case 3 :
					text = handle.getExpression( );
					break;
				case 4 :
					String value = handle.getAggregrateOn( );
					if ( value == null )
						text = NONE;
					else
						text = value;
					break;
			}
			if ( text == null )
			{
				text = ""; 
			}
			return text;
		}
		public void addListener( ILabelProviderListener listener )
		{
		}
		public void dispose( )
		{
		}
		public boolean isLabelProperty( Object element, String property )
		{
			return false;
		}