There are now two internal strategies to bump the fee of a txn.
bump fee method 1: keep all inputs, keep all not is_mine outputs,
allow adding new inputs
bump fee method 2: keep all inputs, no new inputs are added,
allow decreasing and removing outputs (change is decreased first)
Method 2 is less "safe" as it might end up decreasing e.g. a payment to a merchant;
but e.g. if the user has sent "Max" previously, this is the only way to RBF.
We try method 1 first, and fail-over to method 2.
Previous versions always used method 2.
fixes#3652
d0a43662bd