Use XMLHttpRequest directly

jQuery uses getAllResponseHeaders function for getting response headers,
even for getResponseHeader. As far as I know, there is no easy way to
get original xhr object and call getResponseHeader on such object.
Because of that getResponseHeader is broken on firefox with CORS.

I rewrote Travis.ajax to use XMLHttpRequest directly in order to fix
this, the compatibility with jQuery.ajax is mostly handled.

assets/scripts/lib/travis/ajax.coffee

@@ -5,7 +5,7 @@ Travis.ajax = Em.Object.create
 
   DEFAULT_OPTIONS:
     accepts:
-      json: 'application/vnd.travis-ci.2+json'
+      json: 'application/json; version=2'
 
   get: (url, callback) ->
     @ajax(url, 'get', success: callback)
@@ -14,6 +14,7 @@ Travis.ajax = Em.Object.create
     @ajax(url, 'post', data: data, success: callback)
 
   needsAuth: (method, url) ->
+    return true if Travis.ajax.pro
     return true if method != 'GET'
 
     result = @publicEndpoints.find (pattern) ->
@@ -23,6 +24,7 @@ Travis.ajax = Em.Object.create
 
   ajax: (url, method, options) ->
     method = method.toUpperCase()
+
     endpoint = Travis.config.api_endpoint || ''
     options = options || {}
 
@@ -31,7 +33,7 @@ Travis.ajax = Em.Object.create
       options.headers ||= {}
       options.headers['Authorization'] ||= "token #{token}"
 
-    options.url = "#{endpoint}#{url}"
+    url = "#{endpoint}#{url}"
     options.type = method
     options.dataType = options.dataType || 'json'
     options.context = this
@@ -43,15 +45,56 @@ Travis.ajax = Em.Object.create
       options.contentType = options.contentType || 'application/json; charset=utf-8'
 
     success = options.success || (->)
-    options.success = (data) =>
+    options.success = (data, status, xhr) =>
       Travis.lookup('controller:flash').loadFlashes(data.flash) if data?.flash
       delete data.flash if data?
       success.apply(this, arguments)
 
     error = options.error || (->)
-    options.error = (data) =>
+    options.error = (data, status, xhr) =>
       Travis.lookup('controller:flash').pushObject(data.flash) if data?.flash
       delete data.flash if data?
       error.apply(this, arguments)
 
-    $.ajax($.extend(options, Travis.ajax.DEFAULT_OPTIONS))
+    options = $.extend(options, Travis.ajax.DEFAULT_OPTIONS)
+
+    if options.data && (method == "GET" || method == "HEAD")
+      params = []
+      for key, value of options.data
+        params.pushObject("#{key}=#{value}")
+
+      params = params.join '&'
+      delimeter = if url.indexOf('?') == -1 then '?' else '&'
+      url = url + delimeter + params
+
+    xhr = new XMLHttpRequest()
+
+    xhr.open(method, url)
+
+    if options.accepts
+      accepts = []
+      for key, value of options.accepts
+        accepts.pushObject(value)
+      xhr.setRequestHeader('Accept', accepts.join(', '))
+
+    if options.headers
+      for name, value of options.headers
+        xhr.setRequestHeader(name, value)
+
+    if options.contentType
+      xhr.setRequestHeader('Content-Type', options.contentType)
+
+    xhr.onreadystatechange = ->
+      if xhr.readyState == 4
+        contentType = xhr.getResponseHeader('Content-Type')
+        data = if contentType && contentType.match /application\/json/
+          jQuery.parseJSON(xhr.responseText)
+        else
+          xhr.responseText
+
+        if xhr.status >= 200 && xhr.status < 300
+          options.success.call(options.context, data, xhr.status, xhr)
+        else
+          options.error.call(data, xhr.status, xhr)
+
+    xhr.send(options.data)