PicsPage.php

<?php

class PicsPage extends Page
{
	private static $many_many = array(
		"Slider" => "Slider"
	);

	private static $many_many_extraFields = array(
		"Slider" => array(
			"Sorting" => "Int"
		)
	);

}

class PicsPage_Controller extends Page_Controller
{
	public function getCMSFields()
	{
		$fields = parent::getCMSFields();

		$fields->addFieldToTab(
			"Root.Slider",
			new GridField("Slider", "Slider", $this->Slider(),
				$slider = new GridFieldConfig_RelationEditor())
		);

		$slider->addComponent(new GridFieldSortableRows("Sorting"));
		$fields->removeByName("Content");

		return $fields;
	}

	public function Slider() {
		return $this->getManyManyComponents("Slider")->sort("Sorting");
	}

}