Mongo clients with the same settings should be shared since they manage a connection pool.

Also, I removed old code that was supposed to support Pymongo<2.1 which we don't support anymore.

tests/test_connection.py

@@ -34,6 +34,17 @@ class ConnectionTest(unittest.TestCase):
         conn = get_connection('testdb')
         self.assertTrue(isinstance(conn, pymongo.mongo_client.MongoClient))
 
+    def test_sharing_connections(self):
+        """Ensure that connections are shared when the connection settings are exactly the same
+        """
+        connect('mongoenginetest', alias='testdb1')
+
+        expected_connection = get_connection('testdb1')
+
+        connect('mongoenginetest', alias='testdb2')
+        actual_connection = get_connection('testdb2')
+        self.assertIs(expected_connection, actual_connection)
+
     def test_connect_uri(self):
         """Ensure that the connect() method works properly with uri's
         """