Support all download methods in the imagecache formatter

You might or might not know that imagecache, since recently, also supports private downloads and unclean URLs.

That means that imagecache URLs may not only be in the form "[filedir]/imagecache/..." but also in the form "system/files/imagecache/...", for both clean and unclean URLs. Which in turn means that it would be a good thing to use file_create_url() everywhere in the formatter, including the link to the original image in l(). And as l() also copes with external URLs like the ones generated by file_create_url(), it should be absolutely no problem to wrap file_create_url() around the filepath.

Please review, and if possible apply, the attached one-liner. Thanks!