`in` lookup type no longer works with tuples

[jbronn]

When using a tuple parameter, instead of a list, the in lookup type will raise an exception:

>>> MyModel.objects.filter(name__in=['Foo', 'Bar'])
[<MyModel: Foo>, <MyModel: Bar>]
>>> MyModel.objects.filter(name__in=('Foo', 'Bar'))
Traceback (most recent call last):
  ...
  File "/Users/jbronn/django/queryset-refactor/django/db/models/query.py", line 28, in __repr__
    return repr(list(iter(self)))
  File "/Users/jbronn/django/queryset-refactor/django/db/models/query.py", line 46, in __iter__
    self._fill_cache()
  File "/Users/jbronn/django/queryset-refactor/django/db/models/query.py", line 446, in _fill_cache
    self._result_cache.append(self._iter.next())
  File "/Users/jbronn/django/queryset-refactor/django/db/models/query.py", line 127, in iterator
    for row in self.query.results_iter():
  File "/Users/jbronn/django/queryset-refactor/django/db/models/sql/query.py", line 163, in results_iter
    for rows in self.execute_sql(MULTI):
  File "/Users/jbronn/django/queryset-refactor/django/db/models/sql/query.py", line 1301, in execute_sql
    cursor.execute(sql, params)
  File "/Users/jbronn/django/queryset-refactor/django/db/backends/util.py", line 18, in execute
    return self.cursor.execute(sql, params)
ProgrammingError: syntax error at or near "Foo"
LINE 1: ...."name" FROM "tmp_mymodel" WHERE "tmp_mymodel"."name" IN Foo

I believe changes in r7170 to ​where.py are causing the problem.