- remove the PTL_RPC_TYPE_* in favour of PTL_RPC_MSG_*

- remove the PTL_RPC_TYPE_* in favour of PTL_RPC_MSG_*
- request->rq_type is used to tell the rpc subsystem which buffers to use, so
  users of ptlrpc set that
- ptlrpc will fill in request->rq_reqmsg->type or repmsg->type, so it's now
  done in exactly one place
- it was impossible to get PTL_RPC_MSG_ERR before, because we clobbered it in
  ptlrpc_reply; fixed.
- move the incoming-request type verification into the service
- add some incoming-reply type verification to ptlrpc_queue_wait.  Just in case.