[!!!][TASK] Do not add JSON to header if type equals "json"

If you choose "json" as contentType in AJAX-Calls the encoded
json-string will be pushed to the HTTP-Header and will be
outputted on the website. But HTTP-Header is not the right
place for huge json-strings.
So this patch lets "json" works like "jsonbody".

Back in the days, JSON data in the X-JSON header
was for prototypeJS usage, which is now not used
anymore for AJAX requests within the core.

Resolves: #50509
Releases: master
Change-Id: I782cdf2817e30f2e5f016fa92edb06f1e8cbd5b2
Reviewed-on: http://review.typo3.org/22655
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>

typo3/sysext/core/Classes/Http/AjaxRequestHandler.php

@@ -239,7 +239,7 @@ protected function renderAsXML() {
 	 * in your AJAX options of your AJAX request object in JS
 	 *
 	 * the content will be available
-	 * - in the second parameter of the onSuccess / onComplete callback (except when contentFormat = 'jsonbody')
+	 * - in the second parameter of the onSuccess / onComplete callback
 	 * - and in the xhr.responseText as a string (except when contentFormat = 'jsonhead')
 	 * you can evaluate this in JS with xhr.responseText.evalJSON();
 	 *
@@ -248,9 +248,11 @@ protected function renderAsXML() {
 	protected function renderAsJSON() {
 		$content = json_encode($this->content);
 		header('Content-type: application/json; charset=utf-8');
-		header('X-JSON: ' . ($this->contentFormat != 'jsonbody' ? $content : TRUE));
 		// Bring content in xhr.responseText except when in "json head only" mode
-		if ($this->contentFormat != 'jsonhead') {
+		if ($this->contentFormat === 'jsonhead') {
+			header('X-JSON: ' . $content);
+		} else {
+			header('X-JSON: true');
 			echo $content;
 		}
 	}