And unquoted-printing string contains a string to `display` in all
print modes. Although it could be implemented with a structure type
that has a printing function, `raise-arguments-error` further treats
unquoted-printing strings specially by not using the error value
conversion handler, so it reliably produces literal text in the error
message; that way, `raise-arguments-error` can be used to construct
more error messages.
Port `examples`, `interactions`, etc., to use the new `examples`
form of `scribble/examples`. The main intended effect is to ensure
that errors are produced by examples only as specifically
indicated.
