dnssec-signzone ZSK smooth rollover
When signing with a ZSK, check if it has a predecessor. If so, and if the predecessor key is sane (same algorithm, key id matches predecessor value, is zsk), check if the RRset is signed with this key. If so, skip signing with this successor key. Otherwise, do sign with the successor key.
Closes #1551 (closed)
Edited by Matthijs Mekking