Fixed debug code for the middletouch pass in the gc.

Rev: src/array.c:1.87
Rev: src/gc.h:1.65
Rev: src/mapping.c:1.105
Rev: src/multiset.c:1.28
Rev: src/object.c:1.148
Rev: src/program.c:1.272
Rev: src/stralloc.c:1.100