Add application_name to PostgreSQL driver

PostgreSQL allows the user to set the application_name is connecting
to database. It is useful for monitoring purposes.
Currently one could just manually add 'application_name=foo' to DSN,
but having a parameter eases setting it using DoctrineBundle.

docs/en/reference/configuration.rst

@@ -259,6 +259,8 @@ pdo\_pgsql
    the server's certificate will be verified to be signed by one of these
    authorities.
    See http://www.postgresql.org/docs/9.0/static/libpq-connect.html#LIBPQ-CONNECT-SSLROOTCERT
+-  ``application_name`` (string): Name of the application that is
+   connecting to database. Optional. It will be displayed at ``pg_stat_activity``.
 
 PostgreSQL behaves differently with regard to booleans when you use
 ``PDO::ATTR_EMULATE_PREPARES`` or not. To switch from using ``'true'``

lib/Doctrine/DBAL/Driver/PDOPgSql/Driver.php

@@ -103,6 +103,10 @@ class Driver extends AbstractPostgreSQLDriver
             $dsn .= 'sslrootcert=' . $params['sslrootcert'] . ' ';
         }
 
+        if (isset($params['application_name'])) {
+            $dsn .= 'application_name=' . $params['application_name'] . ' ';
+        }
+
         return $dsn;
     }