Add CLI support for restore endpoint.

+ Add the relevant parts to the command line tool and the client
  package.
+ Small improvements to cryptor's restore function:
  + Don't try to restore if the store is already active.
  + Flush the persistence key cache once the restoration occurs.
+ The redoctober program now explicitly mentions that a config file is
  invalid when that's the case.

cmd/ro/main.go

@@ -45,6 +45,7 @@ var commandSet = map[string]command{
 	"order":       command{Run: runOrder, Desc: "place an order for delegations"},
 	"owners":      command{Run: runOwner, Desc: "show owners list"},
 	"status":      command{Run: runStatus, Desc: "show Red October persistent delegation state"},
+	"restore":     command{Run: runRestore, Desc: "perform a restore delegation"},
 }
 
 func registerFlags() {
@@ -132,6 +133,29 @@ func runDelegate() {
 	fmt.Println(resp.Status)
 }
 
+func runRestore() {
+	req := core.DelegateRequest{
+		Name:     user,
+		Password: pswd,
+		Uses:     uses,
+		Time:     duration,
+	}
+
+	resp, err := roServer.Restore(req)
+	processError(err)
+
+	if resp.Status != "ok" {
+		fmt.Fprintf(os.Stderr, "failed: %s\n", resp.Status)
+		os.Exit(1)
+	}
+
+	var st core.StatusData
+	err = json.Unmarshal(resp.Response, &st)
+	processError(err)
+
+	fmt.Println("Restore delegation complete; persistence is now", st.Status)
+}
+
 // TODO: summary response needs better formatting
 func runSummary() {
 	req := core.SummaryRequest{