(SHM-jemalloc) Removed an INFO-severity logged message that is logged from ipc::shm::arena_lend::jemalloc::Ipc_arena::get_collection_id(), a public API but more likely invoked internally from Shm_session::lend_object() which can be oft-used directly and/or for each capnp-encoded message sent through a SHM-jemalloc-backed ipc::transport::struc::Channel. / Use move-semantics in a few places internally to avoid unnecessary shared_ptr ref-count arithmetic. / Effectively remove a few redundant internal assert()s. / Comment and/or doc changes. #144