Bug 390669 [Accessibility]Press 'Tab' doesn't focus on the next report item when adding relative period aggregation.
xtab/org.eclipse.birt.report.item.crosstab.ui/src/org/eclipse/birt/report/item/crosstab/internal/ui/dialogs/CrosstabBindingDialogHelper.java
calculationComposite = new Group( composite, SWT.NONE );
		calculationComposite.setText( CALCULATION_GROUP );
		GridData gridData = new GridData( GridData.FILL_HORIZONTAL );
		gridData.horizontalSpan = 4;
		
		calculationComposite.setLayoutData( gridData );
		GridLayout layout = new GridLayout( );
		
		
		layout.numColumns = 5;
		Layout parentLayout = calculationComposite.getParent( ).getLayout( );
		if ( parentLayout instanceof GridLayout )
			layout.horizontalSpacing = ( (GridLayout) parentLayout ).horizontalSpacing;
		calculationComposite.setLayout( layout );
		Label calculationLable = new Label( calculationComposite, SWT.NONE );
		calculationLable.setText( CALCULATION_TYPE );
		GridData gd = new GridData( );
		gd.widthHint = lbName.computeSize( SWT.DEFAULT, SWT.DEFAULT ).x
				- layout.marginWidth
				- 3;
		calculationLable.setLayoutData( gd );
		calculationType = new Combo( calculationComposite, SWT.BORDER
				| SWT.READ_ONLY );
		gd = new GridData( GridData.FILL_HORIZONTAL );
		gd.horizontalSpan = 4;
		calculationType.setLayoutData( gd );
		calculationType.setVisibleItemCount( 30 );
		calculationType.addSelectionListener( new SelectionListener( ) {
			public void widgetDefaultSelected( SelectionEvent arg0 )
			{