use json as the default content-type for requests from jquery.couch.js

git-svn-id: https://svn.apache.org/repos/asf/couchdb/trunk@961854 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/jquery.couch.js b/jquery.couch.js
index ab8db00..b009af6 100644
--- a/jquery.couch.js
+++ b/jquery.couch.js
@@ -595,6 +595,7 @@
 
   function ajax(obj, options, errorMessage, ajaxOptions) {
     options = $.extend({successStatus: 200}, options);
+    ajaxOptions = $.extend({contentType: "application/json"}, ajaxOptions);
     errorMessage = errorMessage || "Unknown error";
     $.ajax($.extend($.extend({
       type: "GET", dataType: "json", cache : !$.browser.msie,