set the default content type to application/xml

So when I removed content type I made a huge mistake! In our code we had a monkey patch for something @combhua added, so when I tested it on an application it worked fine because I didn't actually test my changes! I found that using no content type gives 415, and that using text/xml gives strange errors. I've made an additional change with the configurable content type to set the default to application/xml, which I can see is working. If that doesn't work for a majority of people the default can be changed, but for now I've verified it works with my crowd server / application.