Made the array list acyclic like the rest of the double linked list. Makes

things simpler, and I want in the gc to be able to tell a pointer that have
visited zero arrays from one that have visited all of them, without special
cases.

Rev: src/array.c:1.154
Rev: src/array.h:1.55
Rev: src/gc.c:1.241
Rev: src/main.c:1.191