- Changed algorithm for determining alive/dead state of peers.

- Changed algorithm for determining alive/dead state of peers.
  Instead of using a fixed number of unacknowledged ICP replies,
  it is now based on timeouts.  If there are no ICP replies
  received from a peer within 'dead_peer_timeout' seconds, then
  we call it dead.
- Added calls to getCurrentTime() in comm_{select,poll}_incoming().
- Fixed shutdown bug when the incoming and outgoing ICP socket is
  the same file descriptor.