Magically make opening files and dirs from chromium work

1. Change to base-files adds a script to /etc/profile.d to automatically run xdg-user-dirs{-,gtk}-update on login if it hasn't been run already (fixes several things in gnome).

2. Change to gvfs adds a symlink called "gnome-open" pointing to gvfs-open, which replaces the old "gnome-open" cmd from libgnome2 (obsolete).  This is needed by xdg-open in many cases where a program (like chromium) tries to open a URI in the session (such as clicking a completed download), etc.