Fixed bug 3245 (When an empty folder is visited, the throbbing
	never stops), bug 2540 (Hook up done_loading signal in
	NautilusMergedDirectory?), and bug 3067 (throbber doesn't start
	again if you do a new "underway" call after load is complete).

	* src/file-manager/fm-directory-view.c: (queue_pending_files):
	Get rid of code that uses nautilus_directory_are_all_files_seen
	to notice we are done loading.
	(done_loading_callback): Use done_loading signal to notice we
	are done loading.
	(finish_loading_uri): Connect to the done_loading signal.
	(disconnect_model_handlers): Disconnect from the done_loading
	signal.

	* libnautilus-extensions/nautilus-merged-directory.c:
	(done_loading_callback),
	(nautilus_merged_directory_add_real_directory),
	(nautilus_merged_directory_remove_real_directory): Add code to
	track all the trash directories and emit done_loading signals
	once all of them are done loading.

	* src/nautilus-window-manage-views.c: (change_state...