Finished task 174 (Use deferred calculation to compute directory
	counts).

	* libnautilus-extensions/Makefile.am:
	* libnautilus-extensions/nautilus-file-attributes.h:
	Added a header file for names of file attributes.

	* libnautilus-extensions/nautilus-directory-private.h:
	* libnautilus-extensions/nautilus-directory.c:
	* libnautilus-extensions/nautilus-directory.h:
	* libnautilus-extensions/nautilus-file-private.h:
	* libnautilus-extensions/nautilus-file.c:
	* libnautilus-extensions/nautilus-file.h:
	Added background computation of the "directory item count"
	attribute. This is serving as a test case for the API for
	requesting additional information.

	* src/file-manager/fm-directory-view.c:
	(display_selection_info): Changed to use the new interface that
	can sometimes return "I don't know" for the number of items in
	a particular directory.
	(stop_load), (done_loading), (display_pending_files),
	(fm_directory_view_stop): Fixed a mistake in the old code where
	we stopped monitoring once the files were discovered. We need to
	keep monitoring.
	(finish_loading_uri): Pass in an attribute that we want to monitor:
	NAUTILUS_FILE_ATTRIBUTE_DIRECTORY_ITEM_COUNT.