BaseCache now has a no-op close method as per ticket #18582

Also removed the hasattr check when firing request_finished signal for
caches with a 'close' method. Should be safe to call `cache.close`
everywhere now

tests/regressiontests/cache/tests.py

@@ -266,6 +266,10 @@ class BaseCacheTests(object):
         self.assertEqual(self.cache.get('answer'), 32)
         self.assertRaises(ValueError, self.cache.decr, 'does_not_exist')
 
+    def test_close(self):
+        self.assertTrue(hasattr(self.cache, 'close'))
+        self.cache.close()
+
     def test_data_types(self):
         # Many different data types can be cached
         stuff = {