o Minor features (security, OOM):
    - When closing an edge connection because we've run out of memory,
      also count the amount of memory that any tunnelled directory
      connection attached to that connection had consumed. Part of
      ticket 11792.

    - When considering whether we're running low on memory, consider
      memory that was allocated as part of zlib buffers as well.
      Count that memory as reclaimed by our OOM handler. Part of
      ticket 11792.

    - When handling out-of-memory conditions, also look at
      non-tunnneled directory connections, and kill the ones that have
      had data sitting on them for the longest. Part of ticket 11792.