use a custom-allocator and detect almost as many errors as you could detect if
you used malloc/new/new[]. (eg. leaks detected, free errors, free mismatch,
etc).
Had to fiddle with mac_malloc_wrappers.c a bit to factor out the appropriate
code to be called from the client request handling code. Also had to add a
new element `MAC_AllocCustom' to the MAC_AllocKind type.
Also added a little documentation, and a regression test.
git-svn-id: svn://svn.valgrind.org/valgrind/trunk@1643
