Fixed a bug

Fixed an exception error that happens when someone adds a tag in a
different case, when a tag already exists in another case. In other
words when someone submits a new tag that creates the same slug as an
existing tag.

taggit/models.py

@@ -5,6 +5,7 @@
 from django.db.models.query import QuerySet
 from django.template.defaultfilters import slugify as default_slugify
 from django.utils.translation import ugettext_lazy as _, ugettext
+from psycopg2 import InternalError
 
 
 class TagBase(models.Model):
@@ -39,7 +40,7 @@ def save(self, *args, **kwargs):
                     res = super(TagBase, self).save(*args, **kwargs)
                     transaction.savepoint_commit(sid, **trans_kwargs)
                     return res
-                except IntegrityError:
+                except (InternalError, IntegrityError):
                     transaction.savepoint_rollback(sid, **trans_kwargs)
                     self.slug = self.slugify(self.name, i)
         else: