du: read and process --files0-from= input a name at a time,

du: read and process --files0-from= input a name at a time,

rather than by reading the entire input into memory and *then*
processing each file name.
* src/du.c: Include "argv-iter.h", not "readtokens0.h".
(main): Rewrite to use argv-iter.
Call xfts_open on each argument, rather than on the entire
argv list at once.
Call print_size here, not from du_files.
Diagnose read failure.
* NEWS (Bug fixes): Mention it.
* THANKS: update.
Reported by Barry Kelly.  More details in
http://article.gmane.org/gmane.comp.gnu.core-utils.bugs/15159/