ALEXANDRIA — It's "full steam ahead" at the Douglas County Historical Society for the summer. That's because the DCHS has just unveiled a new photo exhibit that covers railroads in Douglas County. An open house to launch the exhibit was held at the historical society, 1219 Nokomis St., last week. Jenna Collins, associate director at the DCHS, said the exhibit grew out of a recent artifact chat that was held at the museum. It was hard to choose w…