get all keys of a hash, good for diffing hashes that are equivalent regardless of values

gistfile1.txt

def nested_keys(h)
  th = {"keys" => h.keys.sort}
  h.each{|k,v| th[k] = nested_keys(h[k]) if h[k].class == Hash }
  th
end

nested_keys(h1).diff(nested_keys(h2))