resizedisk will adjust the media size in the headers, whereas
recover simply copies the existing header over the missing one.
XXX recover and resizedisk should probably be merged (even if just
partially, so that recover can properly handle media size changes).
Also, reading in the GPT should probably be centralised so that
error handling can be centralised, and users aren't given misleading
messages (i.e. they aren't told to run recover when they should be
running resizedisk). However, something that can be quickly pulled
up to netbsd-7 was needed, and there isn't time for a major overhaul
or rewrite.
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