[1.5.x] Fixed #19391 -- Oracle specific failure in tests

The failure was caused by using None as a choice for a CharField. To
avoid Oracle's "" <-> NULL handling the field type was changed to
IntegerField.

Backpatch of 632cf32b43

tests/regressiontests/admin_views/models.py

@@ -662,5 +662,5 @@ class Simple(models.Model):
     """
 
 class Choice(models.Model):
-    choice = models.CharField(max_length=1, blank=True, null=True,
-        choices=(('y','Yes'), ('n','No'), (None, 'No opinion')))
+    choice = models.IntegerField(blank=True, null=True,
+        choices=((1, 'Yes'), (0, 'No'), (None, 'No opinion')))