RubyFile and RubyFileTest do not always properly generate Unicode string representations of filenames. Operations like File.exist?, File.file? or File.unlink fail when containing some "weird" characters.
For instance this breaks attachment_fu: Users cannot upload files with those characters in the filename (like German "umlaute": öäü). For the record: attachment_fu needs File.file? and File.unlink. The attached patch fixes those two methods and makes attachment_fu happy, but there are a lot more remaining cases like this in RubyFile. I didn't change these in the patch beause of potantial performance hits cause by the Unicode handling??