du,chgrp,chmod,chown: use FTS_DEFER_STAT

du,chgrp,chmod,chown: use FTS_DEFER_STAT

* src/du.c (main): Use FTS_DEFER_STAT, for better locality of inode
reference.  Important when traversing file systems with fake inodes.
* src/chgrp.c (main): Likewise.
* src/chmod.c (main): Likewise.
* src/chown.c (main): Likewise.
The only remaining fts client, chcon, doesn't need this, since it goes
further and uses FTS_NOSTAT, which suppresses all non- directory
stat calls.