make sure InsertEldestLink always computes a KID
make sure InsertEldestLink always computes a KID

Closes https://github.com/keybase/go/issues/190.

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client