test failure on CCL

[cosmos72]

The MEM-STRING test, newly added to the experimental branch, fails on all known versions of Clozure Common Lisp (CCL) with:
Failure Details:

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MEM-STRING []:
Unexpected Error: #<TYPE-ERROR #x302001BBFF6D>
The value NIL is not of the expected type CHARACTER...

---

Reason: on CCL, (CODE-CHAR #xFFFE) and (CODE-CHAR #xFFFF) both return NIL, while hyperluminal-mem expects them to return the corresponding characters.

The author is discussing the point, which involves the meaning and expected behaviour of Unicode "noncharacters" (U+FFFE U+FFFF and 64 others), on CCL bug tracker http://trac.clozure.com/ccl/ticket/1278

[cosmos72]

After some reasoning (and curses at the insane name "noncharacter" for these Unicode codepoints), CCL developers agreed that the most appropriate action is to change CODE-CHAR behaviour.
It is being modified in order for (CODE-CHAR #xFFFE) to return #\U+FFFE and (CODE-CHAR #xFFFF) to return #\U+FFFF instead of NIL