imapserver: add a tls_level option

Allow the user to block usage of known-bad versions of SSL and TLS.

Signed-off-by: Ben Boeckel <mathstuf@gmail.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/repository/IMAP.py

@@ -246,6 +246,9 @@ class IMAPRepository(BaseRepository):
             raise OfflineImapError(reason, OfflineImapError.ERROR.REPO)
         return cacertfile
 
+    def gettlslevel(self):
+        return self.getconf('tls_level', 'tls_compat')
+
     def getsslversion(self):
         return self.getconf('ssl_version', None)