Usage update.
 [rsc] --rw-rw-r-- M 318707 glenda sys 3421 Dec 15 10:16 sys/src/cmd/du.c
	/n/sourcesdump/2005/1215/plan9/sys/src/cmd/du.c:21,27 - 
	/n/sourcesdump/2005/1216/plan9/sys/src/cmd/du.c:21,27
	  void
	  usage(void)
	  {
	- 	fprint(2, "usage: du [-afnqstu] [-b size] [file...]\n");
	+ 	fprint(2, "usage: du [-afnqstu] [-b size] [file ...]\n");
	  	exits("usage");
	  }