Fixed bug that caused the PDO to throw an invalid keyword error

[brian978]

Without the special case for the sqlsrv driver a PDOException with the following message is thrown: SQLSTATE[IMSSP]: An invalid keyword 'dbname' was specified in the DSN string.

[EvanDotPro]

This is another case where we really need some tests, but this particular class wasn't really written to be easily testable, unfortunately. :-/

We need to figure out if we're going to accept PR's without tests in this case or try to make the class a bit more testable.

[brian978]

We could test up to the point where it cannot connect to the server. Basically the test would check for the issue that is being fixed by the PR.

I was thinking something like this

/**
 * @expectedException \PDOException
 * @expectedExceptionMessage Could not open a connection to SQL Server
 */
public function testDoesNotCauseInvalidKeywordException()
{
    $this->connection->setConnectionParameters(
        array(
            'driver' => 'Pdo_Sqlsrv',
            'database' => 'testdb',
            'username' => 'testname',
            'password' => 'testpass',
            'hostname' => 'testhost',
        )
    );

    try {
        $this->connection->connect();
    } catch(AdapterRuntimeException $e) {
        throw $e->getPrevious();
    }
}

[ralphschindler]

I'll be looking into supporting SQL Server via PDO, which we currently don't.
I'll also take that opportunity to make integration tests for PDO (similar to those in Db2 and Sqlsrv driver tests).