not the numbers themselves.
In t_malloc_printstats(), show information about mapped allocations.
In t_malloc_leaked(), check for leaked mapped allocations. Note that
they would show up anyway since the metadata are allocated from the
bucket allocator, but this makes them more visible.
a caller-provided buffer. Use it to warn about leaks in each individual
test case. Note that we can't fail a test case for leaking, because
individual test cases in a unit may modify shared state which is cleaned
up at the end of the series.
