Racially motivated, civil rights-era killings that are now cold cases will get fresh looks under legislation signed by President Barack Obama. Obama signed the bill Friday. It indefinitely extends a 2007 law that calls for a full accounting of race-based deaths, many of which had been closed for decades. The law was set to expire next year. The bill is named after Emmett Till, a 14-year-old black boy killed in 1955 after whistling at a white woman. His killers were acquitted of murder but later admitted their crimes to a reporter and couldn’t be retried. …