dumpfs(8): add option to only print superblock information

[rew]

Summary

Add an option to dumpfs, -s, that only prints the super block information.

[imp]

This looks good. And I rather like it, since I've wanted something like this in the past.

Strictly speaking, dosb should be a bool, but that's a bigger change because dofreespace, domarshal, and dolabel are not yet bools and should before consistency. And that's well beyond the scope, unless you really wanted to follow up with that. :)

[bcr]

OK from manpages, too. Thanks for addition this feature.

[rew]

In D30881#694691, @imp wrote:

Strictly speaking, dosb should be a bool, but that's a bigger change because dofreespace, domarshal, and dolabel are not yet bools and should before consistency. And that's well beyond the scope, unless you really wanted to follow up with that. :)

Would you rather see a follow-up done as part of this review or in a separate one?