Tweak comment for why usleep is used.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@396656 65c4cc65-6c06-0410-ace0-fbb531ad65f3

tests/test_hashtab_thrash.c

@@ -197,7 +197,9 @@ static void *hash_test_count(void *d)
 		ast_hashtab_end_traversal(it);
 
 		if (last_count == count) {
-			/* Allow other threads to run. */
+			/* Give other threads ample chance to run, note that using sched_yield here does not
+			 * provide enough of a chance and can cause this thread to starve others.
+			 */
 			usleep(1);
 		} else if (last_count > count) {
 			/* Make sure the hashtable never shrinks */