Give checkdisklabel() a new parameter supplying the dev_t of the

Give checkdisklabel() a new parameter supplying the dev_t of the
device whose disklabel is being checked. Within checkdisklabel()
use this information to discover a device name iff (sic) the
label is an obsolete version. Use the name to generate a
meaningful warning message asking the user to rewrite the
disklabel and thus promote it to the current version.

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