Incorrect sequence dropping in PostgreSQL

Currently, DBAL drops the PostgreSQL sequences using the query:

DROP SEQUENCE sequencename

While it is quite correct at the first look, it fails, if the sequence is actually used by a table. Because Doctrine 2 ORM tries to drop the sequences before the tables, it makes impossible to drop a database schema in PostgreSQL due to the following exception:

$ php53 doctrine.php orm:schema-tool:drop
Dropping database schema...
PDOException
SQLSTATE[2BP01]: Dependent objects still exist: 7 ERROR: cannot drop sequence admins_id_seq because other objects depend on it
DETAIL: default for table admins column id depends on sequence admins_id_seq
HINT: Use DROP ... CASCADE to drop the dependent objects too.
/.../Libs/Doctrine/DBAL/Connection.php
Line 570
Trace:
0. PDO::query on line 570
1. Doctrine\DBAL\Connection::executeQuery on line 484
2. Doctrine\ORM\Tools\SchemaTool::dropSchema on line 78
3. Doctrine\ORM\Tools\Console\Command\SchemaTool\DropCommand::executeSchemaCommand on line 59
4. Doctrine\ORM\Tools\Console\Command\SchemaTool\AbstractCommand::execute on line 159
5. Symfony\Component\Console\Command\Command::run on line 205
6. Symfony\Component\Console\Application::doRun on line 117
7. Symfony\Component\Console\Application::run on line 7

A solution is simply to add the "CASCADE" keyword at the end of the query.

Although I encountered this problem on DBAL 2.0-beta4, I checked the most up-to-date code on Git, and the problem is still present there.