be replaced if malloc() et al are replaced by a tool. This is because
different tools implement the function in different ways.
Add an appropriate malloc_usable_size() replacement to each of Memcheck,
Helgrind, DRD, Ptrcheck, Massif.
Update memcheck/tests/malloc_usable and add massif/tests/malloc_usable.
Merged from the DARWIN branch.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@9193