Add some (UN)?LIKELY() to UTF8 handling

It's very rare actually for code to be presented with malformed UTF-8,
so give the compiler a hint about the likely branches.
Fix definition of toCTRL() for EBCDIC

The definition was incorrect.  When going from control to printable
name, we need to go from Latin1 -> Native, so that e.g., a 65 gets
turned into the native 'A'