mstate: use Dead channels rather than Dying for watcher and presence

mstate/unit.go

 package mstate
 
 import (
         "errors"
         "fmt"
         "labix.org/v2/mgo"
         "labix.org/v2/mgo/txn"
         "launchpad.net/juju-core/mstate/presence"
         "launchpad.net/juju-core/trivial"
         "time"
@@ skipping 225 matching lines @@
         u.st.pwatcher.Watch(u.globalKey(), ch)
         defer u.st.pwatcher.Unwatch(u.globalKey(), ch)
         for i := 0; i < 2; i++ {
                 select {
                 case change := <-ch:
                         if change.Alive {
                                 return nil
                         }
                 case <-time.After(timeout):
                         return fmt.Errorf("still not alive after timeout")
-                case <-u.st.pwatcher.Dying():
+                case <-u.st.pwatcher.Dead():
                         return u.st.pwatcher.Err()
                 }
         }
         panic(fmt.Sprintf("presence reported dead status twice in a row for unit %q", u))
 }
 
 // SetAgentAlive signals that the agent for unit u is alive.·
 // It returns the started pinger.
 func (u *Unit) SetAgentAlive() (*presence.Pinger, error) {
         p := presence.NewPinger(u.st.presence, u.globalKey())
@@ skipping 210 matching lines @@
 }
 
 // Config returns the configuration node for the unit.
 func (u *Unit) Config() (config *ConfigNode, err error) {
         config, err = readConfigNode(u.st, u.globalKey())
         if err != nil {
                 return nil, fmt.Errorf("cannot get configuration of unit %q: %v", u, err)
         }
         return config, nil
 }