| old | original path/name of an existing isam file |
| new | new path/name of isam file |
ISTRUE on success, else ISFALSE on error, in which case the error code will be found in the errno global.
isRename will not rename files that are currently in use by other processes.
isRename can be used to move an isam file from one directory to another, but not to a different drive or device.