[COMMIT] Add round-trip tests for my fixed-width-8-bit CCL coding systems, fix a bug with them.

[Aidan Kehoe]

I should mention that you’ll need to remove lisp/mule/*.elc and rebuild
after applying this patch, if you want to do a make check. 
make-8-bit-coding-system is a compiler macro for most coding systems,
because the Unicode mappings when building are availabe at byte-compile-time
but not at dump time.

 Ar an naoú lá is fiche de mí na Samhain, scríobh Aidan Kehoe: 

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-- 
¿Dónde estará ahora mi sobrino Yoghurtu Nghé, que tuvo que huir
precipitadamente de la aldea por culpa de la escasez de rinocerontes?