Fixed #12189 -- Corrected rollback behavior in database cache backend…

…. Thanks to Lakin Wecker for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12409 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/cache/backends/db.py

@@ -65,7 +65,7 @@ def _base_set(self, mode, key, value, timeout=None):
                 cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
         except DatabaseError:
             # To be threadsafe, updates/inserts are allowed to fail silently
-            transaction.rollback()
+            transaction.rollback_unless_managed()
             return False
         else:
             transaction.commit_unless_managed()