Fixed #29870 -- Added DurationField introspection for Oracle and PostgreSQL.

Thanks Tim Graham for the review.

tests/introspection/models.py

@@ -24,6 +24,7 @@ class Reporter(models.Model):
     facebook_user_id = models.BigIntegerField(null=True)
     raw_data = models.BinaryField(null=True)
     small_int = models.SmallIntegerField()
+    interval = models.DurationField()
 
     class Meta:
         unique_together = ('first_name', 'last_name')