unittest: add "just return normally" expectation on results
unittest: add "just return normally" expectation on results

With this expectation, the example form is expected to return normally
(does not signal an error).
This is intended for forms with no expectation specified.

Failure of `(:results :unexpected-error ..)` is modified to support
no specific expectation about returned values.

NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy,NobuoK/xyzzy