Update the error messages

Author: yflory

src/xwiki/RTFrontend/ErrorBox/content.xwiki2

@@ -66,6 +66,7 @@ We were unable to parse the server's response.
 = Save Error =
 
 We were unable to save your document. Try again shortly.
+If this message is displayed everytime you try to save the document, you should consider to **disable the realtime engine** (uncheck the "Allow Realtime Collaboration" checkbox) and **save** again.
 
 )))
 

src/xwiki/RTFrontend/WebHome/attachments/saver.js

@@ -112,6 +112,7 @@ define([
         $.ajax({
             url: url,
             method: 'POST',
+            dataType: "json",
             success: function (data) {
                 try {
                     //var merge=JSON.parse(data);