This is what Jim Harbaugh does. He adds quarterbacks.He did it again Wednesday when the San Francisco 49ers signed veteran Josh Johnson. He was cut Monday by the Bengals, who had drafted AJ McCarron.The 49ers first cut Johnson, who played for Harbaugh at the University of San Diego, during the 2012 preseason. Blaine Gabbert, acquired in a trade in March, is still the favorite to be the backup quarterback to Colin Kaepernick.To make room for Johnson, the 49ers cut defensive lineman Christian Tupou.