[FIXED JENKINS-17085] Bogus requestHeaders value prevented crumb addition.

(Ah, the joys of dynamic typing!)

changelog.html

@@ -55,7 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
-  <li class=>
+  <li class=bug>
+    Preview function for textareas using Jenkins markup did not work when CSRF protection was enabled.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-17085">issue 17085</a>)
 </ul>
 </div><!--=TRUNK-END=-->
 
@@ -79,7 +81,7 @@ Upcoming changes</a>
     Absolute URLs in console output
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-16368">issue 16368</a>)
   <li class=bug>
-    Revert ampersand encoding which can cause backwad incompatibility issue
+    Revert ampersand encoding which can cause backward incompatibility issue
     (<a href="https://github.com/jenkinsci/jenkins/pull/683">pull 683</a>)
   <li class=bug>
     Fix dependency graph computation when upstream build trigger is involved

core/src/main/resources/lib/form/textarea/textarea.js

@@ -34,8 +34,6 @@ Behaviour.specify("DIV.textarea-preview-container", 'textarea', 100, function (e
             };
 
             new Ajax.Request(rootURL + showPreview.getAttribute("previewEndpoint"), {
-                method: "POST",
-                requestHeaders: "Content-Type: application/x-www-form-urlencoded",
                 parameters: {
                     text: text
                 },