Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
I broke an invariant in 11048b893285cf601a224 (it was even nicely documented then). Also clean up the test a bit from while I was debugging it. Fixes #84 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
And some minor cleanup in the process. Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>