add new entities as part of david's checkin.

mail/base/locale/messenger.dtd

@@ -153,6 +153,8 @@
 <!ENTITY sortDescending.accesskey "D">
 <!ENTITY msgsMenu.label "Messages">
 <!ENTITY msgsMenu.accesskey "M">
+<!ENTITY viewThreaded.label "Threaded">
+<!ENTITY viewThreaded.accesskey "T">
 <!ENTITY viewAll.label "All">
 <!ENTITY viewUnread.label "Unread">
 <!ENTITY viewAll.accesskey "A">