Stream class accept all resource types

[weierophinney]

Problem:
Stream accept resource, not only stream resource.
You can initialize stream class with wrong parameter.

Simple(bad) test:

    public function testCanNotInstantiateWithStreamIdentifier()
    {
        $true = false;
        $image = imagecreate(200, 200);

        try {
            $this->stream = new Stream($image, 'wb+');
        } catch(\Exception $e)
        {
            $true = true;
        }

        $this->assertTrue($true); //test is red
    }

Simple (not that bad) solution.

        if (is_resource($stream)) {
            $type = get_resource_type($stream);
            if($type !== 'stream')
            {
                throw new \InvalidArgumentException("Resource is not a stream");
            }
            $this->resource = $stream;
        } elseif (is_string($stream)) {