This looks quite good, I've changed a number of style issues but the only
code I modified was to get rid of a goto in make_new_ds_set() and remove a
small helper function that was only ever called from one place and which
I thought just added a bit of unnecessary confusion.

I'm going to call Tony's code "reviewed", but I'm putting the branch in
the review queue so someone can make sure I didn't dork up those two
changes. They're in commit 7a13d99989b.