r12900 breaks extra() with additional select clauses

[Matthias Kestenholz]

[12900] breaks the following query:

Page.objects.filter(...).extra(select={'_url_length': 'LENGTH(_cached_url)'}).order_by('-_url_length')[0]

LENGTH(_cached_url) is prepended to the list of fields which should be selected, which makes the row tuple one element longer than the fields tuple:

​http://code.djangoproject.com/browser/django/trunk/django/db/backends/mysql/compiler.py#L6

Note that this bug only manifests itself under the following conditions:

1. The first model field is an AutoField
2. The second field is a (Null)?BooleanField
3. The retrieved model has a PK of 1L (0L would also work, but auto incrementing primary key fields never have a value of 0L)

The resulting model instance has True instead of 1L as its PK.

[Matthias Kestenholz]

Now with a regression test