argv has been incremented during argument handling, so elements of the
array are no longer valid. Change the err() arguments so only the
first string pointer in argv is used.
Found during code inspection.
This command can be used by a sysadmin to either copy or migrate a data
file on one DS to another DS.
Its main use is to recover data files onto a mirrored DS after the DS has
been repaired and brought back online.