fails:Array#pack with format 'U' ignores whitespace in the format string
fails:Array#pack with format 'U' calls #to_str to coerce the directives string
fails:Array#pack with format 'U' taints the output string if the format string is tainted
fails:Array#pack with format 'U' calls #to_int to convert the pack argument to an Integer
fails:Array#pack with format 'U' raises a TypeError if #to_int does not return an Integer
fails:Array#pack with format 'U' raises a RangeError if passed a negative number
fails:Array#pack with format 'U' raises a RangeError if passed a number larger than an unsigned 32-bit integer
fails:Array#pack with format 'u' raises a TypeError if passed an Integer
