filefield 5.x-2.3-rc4

Small release, not featuring a lot of changes but still some important ones:

• Support for node revisions - don't have your files magically disappear (yay).
• hook_filefield_widget_settings(), in order to let extension modules hook into the widget settings form.
• #263113: "Has image" should be "Has file".
• #252802: use strtolower for $ext with icons.
• Add application-octet-stream as most basic fallback icon, and rename the x-pdf icon to the more standard application-pdf.

That's it for now, let's see if I can get a hold of dopry in order to coordinate the Drupal 6 port.