capability interface for idl4

[ness]

To get the abstraction we need, there has to be an capability interface 
in idl4. This means, we can say idl4 "here is the cap, give it to xyz", 
and idl4 generates the stub. But I'm a little confused about what ways 
of sending caps we have and what is needed in idl4. I found the 
following ways of sending a capability:

1. simple handle passing
        We simply pass the handle for authentication. This means, the
        server we pass the handle provides the cap.

2. capability copying
        The process a has a handle to a cap provided by s and wants to
        give the process b the right to use this cap. This is done via
        the cap server.

3. sth. mysterious I called capability object passing
        The client calls a server and gets as result a newly created
        handle to a cap. Can e.g. be found in hurd_pm_container_create
        (better to see with the patches by racin).

Looks nice, but is this right this way? And, do we need the second one 
to be provided by idl4? I say, usually the server will not trust its 
client and this it's useless, as the server will not use the new handle.
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-ness-