In an unusual alliance, some Black Alabamans are being joined by their white neighbors in protesting a proposed garbage dump that would be within smelling distance of a stretch of road leading from Selma to Montgomery, Ala., where a pivotal civil rights march took place in 1965. And in an unusual split, some long-time civil rights boosters have come out in favor the landfill, saying it will bring financial help to a poor county. The proposal from a private company to build the landfill was approved last year by the county commission.