new feature: private IPC for every jail

[Robert Watson]

On Tue, 4 Apr 2006, Koen Martens wrote:

> FWIW, I already implemented this once for 5.x a while back, but abandoned 
> the project due to lack of time back then. If no-one else is going to pick 
> this up, i might try and dig up that code again, and port it to 6.x, since 
> this feature is still quite high on my wish list..

Another related, and necessary change, is to fix the field types in our public 
IPC data structures.  Right now they still contain 16-bit ID fields.  We've 
done the first step in separating the user and kernel data structures, but 
we'll need to do the whole compatibility system call thing.  The comment above 
ipc_perm in ipc.h pretty much says it all:

/*
  * XXX almost all members have wrong types.
  */

Robert N M Watson