ALBANY -- Republican leaders were crowing yesterday after a series of battleground-district polls suggested Democrats could lose their one-vote majority in the state Senate in the upcoming elections. The four Siena College surveys showed two incumbent Democrats -- Darrel Aubertine of Watertown and Brian Foley of Long Island -- were neck-and-neck in tough re-election fights. Meanwhile, two veteran Republican senators -- Frank Padavan of Queens and Hugh Farley of Schenectady -- retained wide leads over their Democratic challengers. Democrats have repeatedly cited those two GOP-controlled districts as their best opportunities to even out any losses they might suffer elsewhere in...