Guess file extension based on content-type. When downloading a file, and no path is supplied to store it, guess the file extension using mimetypes and the content-type header. Also supply a unit test for the HotLinkImageForm.

/* preview style examples */
body {
	background-color:#EFEFEF;
	font:70% Verdana, Arial, Helvetica, sans-serif;
}
blockquote {margin:1.5em;color:#666;font-style:italic;}