proc_exception_raise forward and reply port

[Samuel Thibault]

Hello,

In hurd/proc/mgt.c:S_proc_exception_raise(), the proc server forwards
the message to the target thread by calling proc_exception_raise(). In
error cases it returns 0, which msgserver then replies to the requester.
However, if for instance proc_exception_raise() managed to send
the message but failed on reception, the reply port will have been
consumed already, and msgserver erroneously use/deallocate it, so in
such cases we need to return MIG_NO_REPLY since we won't be able to
send a reply anyway. I have to say I'm unable to determine in which
error conditions we need to do that. The one that I encountered was
MACH_RCV_INVALID_NAME.

Samuel