[PATCH] Remove xmalloc-trace and sbrk

Hi all,
  the attached patch removes all references to xmalloc-trace and sbrk.
The former is very rarely used, valgrind is preferred to trace allocations.
The latter is basically useless to detect memory usage on modern OSes which
use other means than brk(2) to obtain memory pages for the heap; it is
actually deprecated on some OSes such as Darwin.

Farm-build-tested.

-- 
    Francesco