in cases where the supplied name was already pointing to a character
special device. This fixes the breakage that occured when trying to
dump a filesystem by name (e. g. /usr), with an fstab already
mentioning the raw device name (like /dev/rda0g) where dump attempted
to use /dev/rrda0g then.
Also removed the now obsolete remark that fstab were carrying block
special names.