refactored pickle everywhere but Session, removed unused imports

gluon/contrib/redis_cache.py

@@ -6,7 +6,10 @@ import redis
 from redis.exceptions import ConnectionError
 from gluon import current
 from gluon.cache import CacheAbstract
-import cPickle as pickle
+try:
+   import cPickle as pickle
+except:
+   import pickle
 import time
 import re
 import logging
@@ -165,7 +168,7 @@ class RedisClient(object):
         expireat = int(time.time() + time_expire) + 120
         bucket_key = "%s:%s" % (cache_set_key, expireat / 60)
         value = f()
-        value_ = pickle.dumps(value)
+        value_ = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
         if time_expire == 0:
             time_expire = 1
         self.r_server.setex(key, value_, time_expire)