Major Description
The ujax file upload support currently uses the MimeTypeService to find out the content type of an uploaded file if no such type is explicitly set. This creates a dependency on the MimeTypeService, requires checking for service availability and more. Better would be for the file upload functionality to use the ServletContext of the UjaxPostServlet to resolve the content type.
In fact, the ServletContext of the UjaxPostServlet uses the MimeTypeService for content type resolution, so we still use the full Sling functionality of content type resolution.