* detach.c (mmalloc_detach): Fix bug in computation of negative

	* detach.c (mmalloc_detach): Fix bug in computation of negative
	brk value.
	* mmcheck.c (mmcheckf): Renamed from mmcheck and new FORCE argument
	added.  Replaced hack that always allowed checking routines to be
 	installed and enforce restriction that they have to be installed
	prior to allocating any memory on the used heap or the FORCE argument
	has to be non-NULL.
	(mmcheck): New function that calls mmcheckf with FORCE set to zero,
	for backwards compatibility.
	* mmalloc.c (malloc): Store result in local variable before
	returning it.  Makes debugging much easier at negligible cost.
	* mmalloc.h (mmcheckf): Declare.
	* attach.c (reuse): Call mmcheckf rather than mmcheck.
	* mmap-sup.c (__mmalloc_mmap_morecore): Improve to allow mmap
	to select a base mapping address if none is otherwise given.
	(mmalloc_findbase): New function that user can call to find
	an available mapping address of a given size.