- we can use EMPTY_LIST only if protocol >= 1

Also: since we are now using EMPTY_LIST only optionally, it is logical
to switch to

	MARK + ... + LIST

instead of

	EMPTY_LIST (or MARK + LIST @proto=0) + MARK + ... + APPENDS

which is at least 1 byte longer.

For the reference - APPENDS is also from protocol 1, while LIST is from
protocol 0.