tests: fix prints
- delete unnecessary newlines
- make sure formatted prints call the formatting routines

R=adg
CC=golang-dev
https://golang.org/cl/2225046
diff --git a/src/pkg/expvar/expvar_test.go b/src/pkg/expvar/expvar_test.go
index 98cd9c2..dc173b9 100644
--- a/src/pkg/expvar/expvar_test.go
+++ b/src/pkg/expvar/expvar_test.go
@@ -76,7 +76,7 @@
 		t.Error("red.Kind() is not a number.")
 	}
 	if x != 3 {
-		t.Error("red = %v, want 3", x)
+		t.Errorf("red = %v, want 3", x)
 	}
 }