ItemsContentProvider: requestMoreItemsSync(): Use HTTPURLConnection instead of HttpClient.

Because it is what we should use now:
http://android-developers.blogspot.co.nz/2011/09/androids-http-clients.html
ItemsContentProvider: loginSync(): Use HttpURLConnection instead of HttpClient.

Because it is what we should use now:
http://android-developers.blogspot.co.nz/2011/09/androids-http-clients.html
Add some null checks.
Correct a log message.
ItemsContentProvider: Extract a method for writing params to a HTTP post.
ItemsContentProvider: UploadAsyncTask: Use HttpURLConnection.

Instead of HttpClient, because that is what we should use now:
http://android-developers.blogspot.co.nz/2011/09/androids-http-clients.html

This seems to work now. We get the HTTP_CREATED success code back,
instead of the circular redirection. I guess there really is a bug
in HttpClient:
http://stackoverflow.com/a/19313384/1123654