apsw and non integer PK
https://github.com/coleifer/peewee/pull/837#issuecomment-175938671
 I see the issue now. Normally, last_insert_id() checks first that the model has an auto incrementing pk.

``` python
def last_insert_id(self, cursor, model):
        if model._meta.auto_increment:
            return cursor.lastrowid
```

This check is missing in the apsw driver, though. Apologies for the confusion on my part. The fix will just need to add this check to the apsw implementation.

the apsw driver currently returns the last [rowid](https://www.sqlite.org/c3ref/last_insert_rowid.html) instead of the las inserted PK, this causes problems for any non int pk (like a UUID)
