A 19-year-old man was shot to death in New Haven on the same street where another man was killed last month. Police say Robert Cirino of New Haven was shot at least twice as he hung on out a porch on Frank Street. Witnesses told police a man approached Cirino, asked ‘‘What’s up?’’, then pulled out a handgun and opened fire when Cirino responded with the same greeting. The man fled on foot. On May 4, 29-year-old Nathan Richardson was also shot to death on Frank Street. No arrest has been made in that killing. Police would not say whether the shootings might be connected. Cirino’s killing was New Haven’s seventh homicide this year.