This function checks for thread support and does a thread initialisation, if the support is available. Also sets the default sync and async gnome-vfs callbacks for various types of authentication.
Note: If you call this, and you use threads with gtk+, you must never hold the gdk lock while doing synchronous gnome-vfs calls. Otherwise an authentication callback presenting a dialog could try to grab the already held gdk lock, causing a deadlock.
Since 2.4