Enable SQUIT command for IRC Operators

Enable SQUIT command for IRC Operators

This patch enables IRC Operators to use the SQUIT command as specified in
RFC 2812, section 3.1.8 "Squit".

When forwarding SQUIT commands, the server connected to the target will
drop the connection (not the target server itself!).

Please note:

 - the configuration option "AllowRemoteOper" mus be enabled on the
   server disconnecting the target to allow forwarding of SQUIT commands.
 - if the remote server is configured to establish the connection, it
   will just do this; so the disconnect is not permanent in this case!