Add PDO::PGSQL_ATTR_DISABLE_PREPARES

[BenMorel]

This constant has been added in PHP 5.6:

https://www.php.net/ChangeLog-5.php

[MaXal]

Please do it this way to provide a correct @since version:

/**
 * @since 5.6
 */
define ('PGSQL_ATTR_DISABLE_PREPARES', 1000);

[BenMorel]

@MaXal Done!