This was quite confusing previously: While calling insert_before()
and then remove_at() properly replaced the current item, calling them the
other way around inserted the new item before the previous item because
remove_at() changed the enumerator's position to the previous item.
The behavior in corner cases (calling the methods before or after
enumeration) is also changed slightly.
This required some refactoring when handling encrypted payloads.
Also changed log messages so that "encrypted payload" is logged instead
of "encryption payload" (even if we internally still call it that) as
that's the name used in RFC 5996.
Its functionality can be replicated by calling insert_before() followed
by remove_at(). Not the other way around, though, because remove_at()
changes the enumerator position.
Tobias Brunner