amd64/67712: Extra informal text when trying to dump but dumpdev is not set.

[Daniel Harris]

Synopsis: Extra informal text when trying to dump but dumpdev is not set.

Responsible-Changed-From-To: freebsd-amd64->julian
Responsible-Changed-By: dannyboy
Responsible-Changed-When: Sat Jul 17 00:27:03 GMT 2004
Responsible-Changed-Why: 
julian added the check in question, before this file was amd64.

http://www.freebsd.org/cgi/query-pr.cgi?pr=67712