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