Add missing import of SSLError exception.

In commit 89cbdc9, usage of SSLError was dropped but later reintroduced
without importing SSLError exception.

Signed-off-by: Arnaud Fontaine <arnau@debian.org>
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/imapserver.py

@@ -26,6 +26,11 @@ import socket
 import base64
 
 from socket import gaierror
+try:
+    from ssl import SSLError
+except ImportError:
+    # Protect against python<2.6, use dummy and won't get SSL errors.
+    SSLError = None
 
 try:
     # do we have a recent pykerberos?