Update file_save_upload to replace existing files

This may be a unique situation, but I have an issue where sometimes temporary files are no longer on the filesystem, so when I upload the csv it finds a filename that it can save it as, but when inserting an entry into the file_managed table, it causes a PDO duplicate entry error. That is because there is an entry in the db table for a file that doesn't exist anymore. With this module, there isn't really a reason to save every csv upload separately, so why not just let it overwrite any existing files? This fixes the error. Patch to come.