Fixed #5598 -- Restored needed imports that were removed in [6333]. Thanks, gav.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@6425 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/sessions/models.py

@@ -1,5 +1,12 @@
-import base64, md5, random, sys, datetime
+import os
+import sys
+import time
+import datetime
+import base64
+import md5
+import random
 import cPickle as pickle
+
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
 from django.conf import settings