fails:Kernel#sprintf passes some tests for positive %x
fails:Kernel#sprintf passes some tests for negative %x
fails:Kernel#sprintf passes kstephens's tests
fails:Kernel#sprintf returns a String in the same encoding as the format String if compatible
fails:Kernel#sprintf returns a String in the argument encoding if format encoding is more restrictive
fails:Kernel#sprintf with negative values with format %x precedes the number with '..'
