Negative UID heuristic fails for UIDs between 2**30 and 2**31

Chef::FileAccessControl considers all UIDs greater than 2**30 to actually be negative UIDs that were wrapped to their radix complements, but this is incorrect, only values greater than 2**31 could possibly be wrapped negative values. This causes failures with strange error messages when a UID between 2**30 and 2**31 is encountered. Luckily, the fix is simple, just set the maximum uid constant in file access control to 1 << 31.