1) rights should be shared by the threads within a process. While it would
be easier to handle this with the struct proc/struct lwp split, we attempt to
do this now by sharing the right lists. Because each right holds a reference
to struct proc, this might cause some problems later.
2) in pthread_exit, really exit the thread. Also reintialize the righ tlist to
make sure we will not destroy the parent's right list
3) rights can hold multiple permissions on a port (ie: send and receive). Fix th
is.
4) first attempt on right carried by messages. We still have to do rights carrie
d in the message body (complex messages).