The idea of the function was to copy out of c string memory into a
lisp string a byte at a time, converting to lisp characters as we go.
However:
* this doesn't work with multibyte charsets
* the underlying deref-array funcall would sometimes pull the entire
array into lisp to then get at the single element-- for each element.
* set elements in the lisp array using schar but there's no guarantee
that the lisp array is a simple-string. Newer SBCL's err on this.