| dest | destination file descriptor |
| source | destination file descriptor |
| key | description of index to cluster on or NULL |
ISTRUE, or ISFALSE, in which case the error code is returned by isErrno, or found in isfd->iserrno
isCopy will copy all records from source into destination, in the order specified by key.
if key is NULL, the current order will be used.
be warned that this call may take some time to run if the file in question is large.