api: Implement RelationUnitsWatcher in client API

state/api/state.go

 // Copyright 2013 Canonical Ltd.
 // Licensed under the AGPLv3, see LICENCE file for details.
 
 package api
 
 import (
         "launchpad.net/juju-core/state/api/agent"
         "launchpad.net/juju-core/state/api/deployer"
         "launchpad.net/juju-core/state/api/machiner"
         "launchpad.net/juju-core/state/api/params"
         "launchpad.net/juju-core/state/api/uniter"
         "launchpad.net/juju-core/state/api/upgrader"
 )
 
 // Login authenticates as the entity with the given name and password.
 // Subsequent requests on the state will act as that entity.  This
 // method is usually called automatically by Open. The machine nonce
 // should be empty unless logging in as a machine agent.
 func (st *State) Login(tag, password, nonce string) error {
-        return st.Call("Admin", "", "Login", &params.Creds{
+        err := st.Call("Admin", "", "Login", &params.Creds{
                 AuthTag:  tag,
                 Password: password,
                 Nonce:    nonce,
         }, nil)
+        if err == nil {
+                st.authTag = tag
+        }
+        return err
 }
 
 // Client returns an object that can be used
 // to access client-specific functionality.
 func (st *State) Client() *Client {
         return &Client{st}
 }
 
 // Machiner returns a version of the state that provides functionality
 // required by the machiner worker.
 func (st *State) Machiner() *machiner.State {
         return machiner.NewState(st)
 }
 
 // Uniter returns a version of the state that provides functionality
 // required by the uniter worker.
 func (st *State) Uniter() *uniter.State {
-        return uniter.NewState(st)
+        return uniter.NewState(st, st.authTag)
 }
 
 // Agent returns a version of the state that provides
 // functionality required by the agent code.
 func (st *State) Agent() *agent.State {
         return agent.NewState(st)
 }
 
 // Upgrader returns access to the Upgrader API
 func (st *State) Upgrader() *upgrader.State {
         return upgrader.NewState(st)
 }
 
 // Deployer returns access to the Deployer API
 func (st *State) Deployer() *deployer.State {
         return deployer.NewState(st)
 }