188.8.131.52: more string trimming fixes
* Return value in the no-op case for non-simple-strings must not be
the underlying simple string object.
* Correct return type (per spec) for STRING-TRIM &co is
STRING-DESIGNATOR, but as long as we take care, we can make it
STRING -- but the old SIMPLE-STRING is still wrong.
* Instead of making WITH-STRING a full-blown Evil Macro, just use
WITH-ARRAY-DATA at the call site.
* Two more test-cases.
patch by James Knight.