A both simpler and more robust gc fix. Should also fix a potential bug that I haven't managed to trig. Rev: src/array.c:1.65 Rev: src/gc.c:1.57 Rev: src/gc.h:1.27 Rev: src/mapping.c:1.73 Rev: src/multiset.c:1.19 Rev: src/object.c:1.105 Rev: src/program.c:1.225 Rev: src/svalue.c:1.67