pdo_dblib closes connection when cursor closes

The PDO connection shouldn't end when the cursor is closed. This behavior was introduced 3 years ago when pdo_dblib was adjusted for multiple rowsets (https://github.com/php/php-src/commit/3a069e814fe01b36812b5c768dd52ccdea3ed098), only on versions 5.4+.

This prevents further queries to the same connection, transactions, the usage of variables and even getting multiple rowsets with that connection (this wasn't working on 5.4.13).

This is a bugfix for https://bugs.php.net/bug.php?id=64522. Tested and the expected results were met. Should be applied to branches PHP-5.4 and PHP-5.5.

Cheers,

Guilherme Capilé