Fixed #14223 -- Extended unification of exception raised in presence of integrity constraint violations.

The unification had been introduced in r12352 and native backend exceptions still
slipped through in cases that end in connection.commit() call. Thanks Alex,
Jacob and Carl for reviewing.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14320 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/backends/models.py

@@ -1,8 +1,7 @@
 from django.contrib.contenttypes import generic
 from django.contrib.contenttypes.models import ContentType
-from django.conf import settings
 from django.db import models
-from django.db import connection, DEFAULT_DB_ALIAS
+from django.db import connection
 
 
 class Square(models.Model):
@@ -55,3 +54,18 @@ class Post(models.Model):
         db_table = 'CaseSensitive_Post'
 
 
+class Reporter(models.Model):
+    first_name = models.CharField(max_length=30)
+    last_name = models.CharField(max_length=30)
+
+    def __unicode__(self):
+        return u"%s %s" % (self.first_name, self.last_name)
+
+
+class Article(models.Model):
+    headline = models.CharField(max_length=100)
+    pub_date = models.DateField()
+    reporter = models.ForeignKey(Reporter)
+
+    def __unicode__(self):
+        return self.headline