A suspect accused of slashing three NYPD cops with a machete has been charged with attempted murder, police said Tuesday. Jean Blain, 40, was also charged with assault, menacing and weapon possession. Police were called to Blain’s New York Ave. apartment near Beverly Road in East Flatbush about 3:20 p.m. Monday because neighbors complained he was acting erratically. Officers first spoke to Blain’s family then moved to arrest him, at which point he attacked, police said. He slashed one cop’s head, police said. As other officers moved toward him he allegedly slashed a second officer on the wrist…