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
IAggrFunction[] choices = getFunctions( );
		if ( choices == null )
			return new String[0];
		String[] displayNames = new String[choices.length];
		for ( int i = 0; i < choices.length; i++ )
		{
			displayNames[i] = choices[i].getDisplayName( );
		}
		return displayNames;
	}
	private IAggrFunction getFunctionByDisplayName( String displayName )
	{
		IAggrFunction[] choices = getFunctions( );
		if ( choices == null )
			return null;
		for ( int i = 0; i < choices.length; i++ )
		{
			if ( choices[i].getDisplayName( ).equals( displayName ) )
			{
				return choices[i];
			}
		}
		return null;
	}
	private String getFunctionDisplayName( String function )
	{
		try
		{
			return DataUtil.getAggregationManager( )
					.getAggregation( function )