In the wake of a pension deal Democratic leaders struck with Gov. Arnold Schwarzenegger, California's prison guards union has dropped $215,000 to oppose Assemblywoman Anna Caballero's quest for the state Senate.Caballero, D-Salinas, is facing Ceres Mayor Anthony Cannella, a Republican, for the 12th Senate District, probably the most contested seat in the Legislature. The race is the top concern for both Senate President Pro Tem Darrell Steinberg, D-Sacramento, and his GOP counterpart, Senate Republican leader Bob Dutton of Rancho Cucamonga. If Caballero wins, Democrats would likely have 26 seats in the upper house, one short of the two-thirds majority now...