More rtldebug to get better info when gc_mark problems happen.

Rev: Makefile:1.168
Rev: src/array.c:1.226
Rev: src/gc.c:1.338
Rev: src/gc.h:1.138
Rev: src/mapping.c:1.214
Rev: src/multiset.c:1.119
Rev: src/object.c:1.304
Rev: src/pike_types.c:1.361
Rev: src/program.c:1.773
Rev: src/svalue.c:1.255