Refactor on File::processNew

Refactor on File::processNew

The code was so involved there was even a comment asking for a refactor.

Now, File_redirection::where always returns a nice File_redirection
object instead of an array or string or nothing.  The object is
either one which already existed or else a new, unsaved object.

Instead of duplicating "does it exist" checks everywhere, do it in
File_redirection::where.  You either get what exists or something to save.

An unsaved File_redirection may be paired with an unsaved File.
You will want to save the File first (using ->saveFile()) and put the
id in File_redirection#file_id before saving.