- Handle the file: and http: URLs also in TileCache.

- Add a document part number parameter to the protocol where
  appropriate. Needed at least for the key, mouse, selecttext and
  selectgrahic client->server messages. Probably also the LOK
  callback server->client messages.

- Have MasterProcessSession::dispatchChild() wait for a child process
  to become available, if none of those that have been (pre-)spawned
  have initialised themselves and reported back yet.

- Make child processes time out and go away when inactive for a while.

- Make the "load" request actually take an URL, not a file name. (But
  for now would always be a file: URL, sure.)

- Investigate using "bind" mounts, remounted read-only, to set up the
  chroot jail, instead of requiring the "sys" template tree to
  traverse and hardlink into the jail.

- Investigate using "seccomp". Not available in the Linux 3.7.10 in
  openSUSE 12.3 for instance, though.

- Add some intentional slowdown option to emulate slow network
  connection.
