Batch exchange withdrawal to lightning requires covenants

Participants in a transaction can double-spend the batch by using a commit tx that spends from the previous funding output. It is important for participants to be aware of this possibility and not use 0-conf on the splice transaction. However, other than that, the splice transaction functions like a regular splice and participants should watch for double-spends while waiting for confirmations. The suggestion to use nVersion=3 and pay 0 fees is not applicable in this case. Instead, a "standard" transaction with a reasonable feerate and nVersion=2 should be used.