want a way to check all umem buffers on process exit
At present UMEM_DEBUG checks umem buffers on the boundary between umem and the client. That is, during allocation or free. For applications that leak considerable amounts of memory (perhaps intentionally) such as ld(1), this negates much of its utility.
We should have a means via UMEM_DEBUG to check all buffers and redzones on process exit to catch what bugs we can in such software.