[RFC][PATCH 0/4] malloc_info: minor fixes and improvements [BZ #17039]

[Ken Milmore]

Now that the FSF have accepted my copyright assigment for glibc, I
thought it might be a good time to resubmit these patches for review.

To recap, the intention is to rectify a couple of problems with the
output of malloc_info(), to make it useful as a more detailed
alternative to mallinfo() and malloc_stats(). Namely:

1. The reported chunk sizes are typically off by a few bytes (BZ#17039)
2. The size(s) of the "top" heap chunk(s) are not accounted for.

There is also a new unit test to check that the respective outputs of
malloc_info and mallinfo agree exactly.

Feedback appreciated.

-Ken.