Removed django incompatibility

Django is using timeout=0 to use default timeout value.

Using timeout=0 to set non-volatile keys conflicts with django API.

redis_cache/cache.py

@@ -130,13 +130,8 @@ class CacheClass(BaseCache):
         Set content expiration, if necessary
         """
         key = self.make_key(key, version=version)
-        if timeout is None:
+        if not timeout:
             timeout = self.default_timeout
-        if timeout <= 0:
-            # force the key to be non-volatile
-            result = self._cache.get(key)
-            self._cache.set(key, result)
-        else:
         # If the expiration command returns false, we need to reset the key
         # with the new expiration
         if not self._cache.expire(key, timeout):

tests/testapp/tests.py

@@ -195,14 +195,6 @@ class RedisCacheTests(TestCase):
         self.cache.set(key, value);
         self.assertTrue(self.cache._cache.ttl(key) > 0)
 
-    def test_set_expiration_timeout_0(self):
-        key, value = self.cache.make_key('key'), 'value'
-        self.cache.set(key, value)
-        self.assertTrue(self.cache._cache.ttl(key) > 0)
-        self.cache.expire(key, 0)
-        self.assertEqual(self.cache.get(key), value)
-        self.assertTrue(self.cache._cache.ttl(key) < 0)
-
     def test_set_expiration_first_expire_call(self):
         key, value = self.cache.make_key('key'), 'value'
         # bypass public set api so we don't set the expiration