apply to the indicated (sender/receiver) side.
- Added the hide/show and protect/risk filter rules as an alternate
  way to specify sender-/receiver-specific include/exclude rules.
- send_rules() now allows f_out to be -1 to indicate that the list
  should be scanned but not sent.
- send_rules() now filters the list to remove any items that don't
  apply to the current side (after sending the item to the other
  side when f_out != -1).
- {send,recv}_filter_list() now transfer the list, even when the
  receiver is the server and --delete-excluded was specified (the
  exchanged list is appropriately filtered, of course).
- recv_filter_list() uses send_rules() to trim non-applicable rules
  when we're a local-server (because we got our filter list without
  send/recv calls when fork() duplicated it).