NEW ORLEANS, June 27 (Reuters) - Poor blacks in New Orleans sued on Tuesday to stop the government from replacing public housing units with mixed-income dwellings, calling it a discriminatory move that would bar them from coming home after Hurricane Katrina. The federal Department of Housing and Urban Development (HUD) plans to raze more than half of the low-income housing units it oversees in the city and replace them over the next few years with units the agency says will be better and safer. "HUD plans to keep low-income black families out of New Orleans," said Judith Browne, co-director of...