New message type FORCE_IPC, which can be sent uding the SENDIPC script
command.  When a client receives FORCE_IPC it calls the ipc script function
if it exists.  i.e.

to send "fish" to a user:

   SENDIPC user fish

that user will then have a function called 'ipc', whcih will be executed
the same as any other event - the text (in this case, 'fish') will appear
as $1 and the USER command will return the name of the sender.