Signing after UPDATE fixed
Fixed changeset signing after UPDATE.
Was ignoring RRSIGs related to a RRSet that was completely removed. This was a relict of old code when RRSIGs were connected to their RRSets.
Also simplified the function (and function sign_rr_should_be_signed()) and did some minor refactoring and polishing. Please try to check if function sign_changeset_wrap() is equivalent to its previous state.