doctrine/dbal — pull request #623 by jgallred (2014-06-25 15:36:40+00:00)
Title: Prevent Connection from maintaining a second reference to an injected PDO object.

Previously, if a developer explicitly closed the Connection, only the _conn reference was destroyed, but the _params['pdo'] reference remained and kept the PDO connection alive. By unsetting the _params reference, we maintain only the _conn reference, exactly as if the PDO connection is generated internally.