Only display the countermeasures message if the -v flag is used.

--- ping_common.c.orig	2007-11-27 01:57:27.000000000 +0100
+++ ping_common.c	2008-05-21 13:54:46.000000000 +0200
@@ -663,7 +663,8 @@
 		tvsub(tv, &tmp_tv);
 		triptime = tv->tv_sec * 1000000 + tv->tv_usec;
 		if (triptime < 0) {
-			fprintf(stderr, "Warning: time of day goes back (%ldus), taking countermeasures.\n", triptime);
+			if (options & F_VERBOSE)
+				fprintf(stderr, "Warning: time of day goes back (%ldus), taking countermeasures.\n", triptime);
 			triptime = 0;
 			if (!(options & F_LATENCY)) {
 				gettimeofday(tv, NULL);