These display bases work to replace unprintable characters so the
name is a misnomer. In addition they are the same option and this
display behaviour is not something that is configurable.
This does not affect encodings because all our internal text strings
need to be valid UTF-8 and the source encoding is specified using
ENC_*.
Remove the assertion for valid UTF-8 in proto.c because
tvb_get_*_string() must return a valid UTF-8 string, always, and we
don't need to assert that, it is expensive.
Jaap Keuter