* NLINE_CAN_CLINE is vapour, nuke the lingering reference to the non-existent

  N:Line flag.
* Fix SQUIT and netsplits so that multiple SQUIT commands aren't propagated
  across the network.  Netsplits now show the *actual* servers being split.
* Only process SQUIT commands coming from the appropriate *uplink* server,
  otherwise pass them forwards for processing.
* A user leaving the network via QUIT wasn't being propagated all the time.
* Cleaned up /STATS u as per DigitalMan's recommendations.
* Don't allow opers without the correct O:Line flags to /SQUIT remote servers,
  among other things.
* Deny incoming NICK commands from any server which has a server mismatch,
  and send out a KILL message for that nick.
* PINGs and PONGs weren't being propagated (as per /SPING in many clients.)
* Fixed client_add and client_remove calls, at the expense of a Synchronet
  port to the C64 and VIC-20.  Sorry guys, we tried :(