* void PREFIX_copy_merged(SORT_KEY **keys, struct fastbuf **data, uns n, struct fastbuf *dest)
* takes n records with keys in memory and data in fastbufs and writes
* a single record. Used only if SORT_DATA_SIZE or SORT_UNIFY_WORKSPACE is defined.
* void PREFIX_copy_merged(SORT_KEY **keys, struct fastbuf **data, uns n, struct fastbuf *dest)
* takes n records with keys in memory and data in fastbufs and writes
* a single record. Used only if SORT_DATA_SIZE or SORT_UNIFY_WORKSPACE is defined.