Fix one more relative import.

src/AccessControl/SecurityManagement.py

@@ -24,7 +24,7 @@ def getSecurityManager():
         nobody = getattr(SpecialUsers, 'nobody', None)
         if nobody is None:
             # Initialize SpecialUsers by importing User.py.
-            import User
+            from . import User
             nobody = SpecialUsers.nobody
         manager = SecurityManager(thread_id, SecurityContext(nobody))
         _managers[thread_id]=manager