OPPOSITION PARTIES in Bulgaria fared no better in this year's fall elections than they did last year. The ruling Bulgarian Socialist Party (BSP), returned to power in last December's parliamentary elections, walked away with most of the seats on local councils and an overwhelming majority of mayor-ships. But this time around, some of the races were much closer - and opposition parties overcame some of their differences to support a single candidate, at least in the second round. The new, albeit hesitant, cooperation could portend a stronger opposition challenge.