In the SHM-jemalloc session glue layer account for the realistic possibility that when one uses session.lend/borrow_object() to transmit native structures residing in SHM, those operations can fail due to session being down at that time. More or less that means (1) correcting a few log messages and comments and (2) do not "helpfully" assert on things that might not always be true. / Comment and/or doc changes.#53