Merge pull request #144 from Flow-IPC/ipc-143_perf-dive

(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.

Author: ygoldfeld