I'm not sure how or why this got changed from the original code, but at some point the code to determine if a file is an image changed from using gtk.gdk.pixbuf_get_file_info(path) to testing the file extension. I tend to have image files without file extensions and so I've had a copy of comix on my system just for that. But I got tired of it and so I dug into the code and fixed it. I can't imagine how this could cause any errors, but I could be wrong. This patch really just replaces the current is_image_file(path) functon with the one from the original comix.This has been bugging me for a while so I just figured I'd try and fix it.