MacDill Air Force Base, Fla., has a serial trespasser. Authorities say a homeless woman has sneaked onto the base four times in eight months, sometimes staying for several days at a time, the Tampa Bay Times reported. The trouble apparently began in October, when a retired Air Force officer who docks his boat at a MacDill marina found a woman on his boat, the paper reported. She had in her hands the boat’s ignition keys. When the retired officer asked her who had given her permission to be aboard, she allegedly told him she had just come from the Pentagon…