I just pushed a series of changes in preparation for upstreaming
mallocng. Before it's actually imported, it can be tested by
performing the following simple 4 steps:

1. mkdir src/malloc/mallocng
2. echo "MALLOC_DIR = mallocng" >> config.mak
3. Dropping the attached files into src/malloc/mallocng
4. Symlinking or copying meta.h, malloc.c, realloc.c, free.c,
   malloc_usable_size.c, and aligned_alloc.c from mallocng source dir
   to src/malloc/mallocng. (You can also include dump.c if desired.)

This produces a near-fully-integrated malloc, including support for
reclaim_gaps donation from ldso. The only functionality missing, which
I expect to flesh out before actual import, is handling of the case of
incomplete malloc replacement by interposition (__malloc_replaced!=0).

Please report any problems encountered.

Rich