the malloc/free level, not within the heap abstraction, and there's a
separate lock to control sbrk access.
Also, get rid of the separate `unmap_free_area' function in free.c, and
just put the code in the `free' function directly, which saves a bunch
of space (even compared to using an inline function) for some reason.
smarter than the old "malloc-simple", and actually works, unlike
the old "malloc". So kill the old "malloc-simple" and the old
"malloc" and replace them with Miles' new malloc implementation.
Update Config files to match. Thanks Miles!
