This adds some image size options and scaling features. The single image upload form now has a Size option with three choices: Thumbnail, Medium and Full Size. Selecting Thumbnail or Medium will automatically add a link to the attachment page if a URL is not specified by the user; Full Size includes no link unless one is specified. The dimensions for thumbnails and medium sized images can be set on the Options/Writing tab.
The images aren't actually resized (yet); browser scaling is used to fit the image within the specified dimensions. There's a filter hook that could be used to create and cache an intermediate sized image file to save bandwidth.
I've also moved some general image functions out of media.php and into a new wp-includes/image.php file. There's still some work that needs to be done in consolidating the single and multi upload forms and code.
