Don't return `true` from view classes' render() method.

It cause's Controller:render() to set the response body as `true`.

Refs #2780

lib/Cake/Test/Case/View/MediaViewTest.php

@@ -80,8 +80,7 @@ class MediaViewTest extends CakeTestCase {
 		$this->MediaView->response->expects($this->once())
 			->method('send');
 
-		$result = $this->MediaView->render();
-		$this->assertTrue($result);
+		$this->MediaView->render();
 	}
 
 /**
@@ -119,8 +118,7 @@ class MediaViewTest extends CakeTestCase {
 		$this->MediaView->response->expects($this->once())
 			->method('send');
 
-		$result = $this->MediaView->render();
-		$this->assertTrue($result);
+		$this->MediaView->render();
 	}
 
 /**

lib/Cake/Test/Case/View/ViewTest.php

@@ -1024,7 +1024,7 @@ class ViewTest extends CakeTestCase {
 		$this->assertRegExp("/<title>yo what up<\/title>/", $result);
 		$this->assertRegExp("/<p><a href=\"flash\">yo what up<\/a><\/p>/", $result);
 
-		$this->assertTrue($View->render(false, 'flash'));
+		$this->assertNull($View->render(false, 'flash'));
 
 		$this->PostsController->helpers = array('Session', 'Cache', 'Html');
 		$this->PostsController->constructClasses();

lib/Cake/View/MediaView.php

@@ -62,7 +62,7 @@ class MediaView extends View {
  *
  * @param string $view Not used
  * @param string $layout Not used
- * @return boolean
+ * @return void
  */
 	public function render($view = null, $layout = null) {
 		$name = $download = $id = $modified = $path = $cache = $mimeType = $compress = null;
@@ -94,7 +94,6 @@ class MediaView extends View {
 			$this->response->compress();
 		}
 		$this->response->send();
-		return true;
 	}
 
 }

lib/Cake/View/View.php

@@ -445,12 +445,12 @@ class View extends Object {
  *
  * @param string $view Name of view file to use
  * @param string $layout Layout to use.
- * @return string Rendered Element
+ * @return string|null Rendered content or null if content already rendered and returned earlier.
  * @throws CakeException If there is an error in the view.
  */
 	public function render($view = null, $layout = null) {
 		if ($this->hasRendered) {
-			return true;
+			return;
 		}
 		$this->Blocks->set('content', '');