Finalize python2/3 codebase compatibility and get rid of 2to3

tests/queryset/test_queryset.py

@@ -110,7 +110,7 @@ class TestQueryset(unittest.TestCase):
         # Filter people by age
         people = self.Person.objects(age=20)
         assert people.count() == 1
-        person = people.next()
+        person = next(people)
         assert person == user_a
         assert person.name == "User A"
         assert person.age == 20
@@ -2768,7 +2768,7 @@ class TestQueryset(unittest.TestCase):
         )
 
         # start a map/reduce
-        cursor.next()
+        next(cursor)
 
         results = Person.objects.map_reduce(
             map_f=map_person,
@@ -4395,7 +4395,7 @@ class TestQueryset(unittest.TestCase):
         # Use a query to filter the people found to just person1
         people = self.Person.objects(age=20).scalar("name")
         assert people.count() == 1
-        person = people.next()
+        person = next(people)
         assert person == "User A"
 
         # Test limit
@@ -5309,7 +5309,7 @@ class TestQueryset(unittest.TestCase):
         if not test:
             raise AssertionError("Cursor has data and returned False")
 
-        queryset.next()
+        next(queryset)
         if not queryset:
             raise AssertionError(
                 "Cursor has data and it must returns True, even in the last item."