add am-imap-advanced, not yet part of product -> no reviewer

mailnews/base/prefs/resources/locale/en-US/am-imap-advanced.dtd

@@ -0,0 +1,8 @@
+<!ENTITY serverDirectory.label "IMAP server directory">
+<!ENTITY usingSubscription.label "Show only subscribed folders">
+<!ENTITY dualUseFolders.label "Server supports folders that contain sub-folders and messages">
+<!ENTITY namespaceDesc.label "These preferences specify the namespaces on your IMAP server">
+<!ENTITY personalNamespace.label "Personal namespace:">
+<!ENTITY publicNamespace.label   "Public (shared):">
+<!ENTITY otherUsersNamespace.label    "Other Users:">
+<!ENTITY allowNamespaceOverride.label "Allow server to override these namespaces">