[regression][patch] dojo.xhr: content-type header is plaintext

[liucougar]

with dojo < 1.8, dojo.xhrPost({url:'someurl',content:{key:'value'}}) would set content-type to application/x-www-form-urlencoded

however, with current trunk, plain/text is set in FF, application/xml in IE

a possible fix is:

dojo/_base/xhr.js

@@ -593 +593 @@
                var options = {
                        method: method,
                        handleAs: "text",
-                       headers: args.headers,
                        data: ioArgs.query,
                        timeout: args.timeout,
                        sync: args.sync,
                        withCredentials: args.withCredentials,
                        ioArgs: ioArgs
                };
+               if(args.headers){
+                       options.headers = args.headers;
+               }
 
                dojo._ioNotifyStart(dfd);
                try{

this is introduced with #15182

[liucougar]

see #15552 for a test case

[Bryan Forbes]

In [29043]:

Fix masked options to dojo/request/xhr in dojo/_base/xhr. refs #15548 !strict

[Bryan Forbes]

Good catch. Thanks, liucougar!