#13 Inconsistent semantics of Append to a list

[Chris Henrich]

in bc-containers-lists-double.adb the procedures
Append(L : in out List; From_List : in out List)
and
Append(L : in out List; From_List : in out List; After : Positive)
raise BC.Not_Root if From_List begins with an item which has other predecessors. This gives a different semantics from singly-linked lists and is unnecessary.