.hidden files and GtkFileChooser

[Federico Mena Quintero <federico ximian com>]

For reference, please see bug #129170.

- Should both the Unix and Gnome-VFS backends for GtkFileSystem parse
the .hidden files on their own, or just the Gnome-VFS one?

- Should gnome-vfs provide this functionality on its own in the future? 
E.g. would it make sense to add a HIDDEN value to GnomeVFSFileFlags for
when you get a GnomeVFSFileInfo?  [In this case, should dotfiles be
flagged as such?]

  Federico