check status of write.

Notes:
Tue Jan 19 15:16:47 EST 2010 geoff
    it's only standard error.


Reference: /n/sources/patch/sorry/sortwrite
Date: Tue Jul 21 03:01:20 CES 2009
Signed-off-by: quanstro@quanstro.net
Reviewed-by: geoff

--- /sys/src/cmd/sort.c	Tue Jul 21 03:00:49 2009
+++ /sys/src/cmd/sort.c	Tue Jul 21 03:00:46 2009
@@ -1430,7 +1430,8 @@
 	k->klen = cl;
 
 	if(args.vflag) {
-		write(2, l->line, l->llen);
+		if(write(2, l->line, l->llen) != l->llen)
+			exits("write");
 		for(i=0; i<k->klen; i++) {
 			fprint(2, " %.2x", k->key[i]);
 			if(k->key[i] == 0x00 || k->key[i] == 0xff)