HEADS UP: slapd outbound connections

["Howard Chu" <hyc@symas.com>]

I've added some code to let slapd manage outbound connections in its main
listener thread. Activity on connections marked SLAP_C_CLIENT are handed off
directly to the thread pool. I've also restructured syncrepl so that it uses
this feature in persist mode.

This approach frees up the thread that would otherwise be tied up in the
persist loop. It also avoids the need to poll on 10-second intervals to
detect slapd shutdown, while still providing immediate response to incoming
changes. Let me know if you see any problems....

  -- Howard Chu
  Chief Architect, Symas Corp.       Director, Highland Sun
  http://www.symas.com               http://highlandsun.com/hyc
  Symas: Premier OpenSource Development and Support