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
return ""; 
			}
			ComputedColumnHandle handle = ( (ComputedColumnHandle) element );
			String value = null;
			if ( COLUMN_NAME.equals( property ) )
			{
				value = handle.getName( );
			}
			else if ( COLUMN_DATATYPE.equals( property ) )
			{
				IChoice type = dataTypeChoiceSet.findChoice( handle.getDataType( ) );
				if ( type != null )
				{
					for ( int i = 0; i < dataTypeDisplayNames.length; i++ )
					{
						if ( dataTypeDisplayNames[i].equals( type.getDisplayName( ) ) )
						{
							return new Integer( i );
						}
					}
				}
				return new Integer( 0 );
			}
			else if ( COLUMN_EXPRESSION.equals( property ) )
			{
				value = handle.getExpression( );
			}
			else if ( COLUMN_AGGREGATEON.equals( property ) )
			{
				value = handle.getAggregrateOn( );;