* malloc/arena.c (ptmalloc_init): Recognize MALLOC_PERTURB_ and call

* malloc/arena.c (ptmalloc_init): Recognize MALLOC_PERTURB_ and call

	mallopt appropriately.
	* malloc/malloc.h: Define M_PERTURB.
	* malloc/malloc.c (perturb_byte): New variable.
	(alloc_perturb, free_perturb): New macros.
	(_int_malloc): Before returning, overwrite the memory if this is
	requested.
	(_int_free): Overwrite freed memory if requested.
	(mALLOPt): Handle M_PERTURB.
	* test-skeleton.c: Add call to mallopt with M_PERTURB command.