non-weak internal cyclic refs didn't get gc'd.

Rev: src/array.c:1.77
Rev: src/gc.c:1.105
Rev: src/gc.h:1.54
Rev: src/mapping.c:1.92
Rev: src/multiset.c:1.24
Rev: src/object.c:1.135
Rev: src/program.c:1.249
Rev: src/queue.c:1.5
Rev: src/queue.h:1.4
Rev: src/svalue.c:1.83
Rev: src/testsuite.in:1.312