Bug #308552 --> land some strings for growl integration in case we add growl support.

mail/locales/en-US/chrome/messenger/messenger.properties

@@ -421,3 +421,7 @@ copyToFolderAgainAccessKey=t
 
 #LOCALIZATION NOTE %1$S is the e-mail address of the person we will allow remote images for
 alwaysLoadRemoteContentForSender=Click here to always load remote images from %1$S.
+
+# Strings for growl notifications on Mac OS X
+subjectNotificationTitle=Subject: "%1$S"
+senderNotificationText=Sender: "%1$S"