all: fix some vet-found printf errors

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7393059

src/pkg/archive/tar/reader_test.go

@@ -338,7 +338,7 @@ func TestParsePAXTime(t *testing.T) {
 			t.Fatal(err)
 		}
 		if !ts.Equal(expected) {
-			t.Fatal("Time parsing failure %s %s", ts, expected)
+			t.Fatalf("Time parsing failure %s %s", ts, expected)
 		}
 	}
 }

src/pkg/encoding/gob/gobencdec_test.go

@@ -348,7 +348,7 @@ func TestGobEncoderFieldsOfDifferentType(t *testing.T) {
 		t.Fatal("decode error:", err)
 	}
 	if y.G.s != "XYZ" {
-		t.Fatalf("expected `XYZ` got %c", y.G.s)
+		t.Fatalf("expected `XYZ` got %q", y.G.s)
 	}
 }
 

src/pkg/encoding/json/decode_test.go

@@ -1158,7 +1158,7 @@ type Time3339 time.Time
 
 func (t *Time3339) UnmarshalJSON(b []byte) error {
 	if len(b) < 2 || b[0] != '"' || b[len(b)-1] != '"' {
-		return fmt.Errorf("types: failed to unmarshal non-string value %q as an RFC 3339 time")
+		return fmt.Errorf("types: failed to unmarshal non-string value %q as an RFC 3339 time", b)
 	}
 	tm, err := time.Parse(time.RFC3339, string(b[1:len(b)-1]))
 	if err != nil {

src/pkg/net/http/request_test.go

@@ -262,7 +262,7 @@ func TestNewRequestContentLength(t *testing.T) {
 			t.Fatal(err)
 		}
 		if req.ContentLength != tt.want {
-			t.Errorf("ContentLength(%#T) = %d; want %d", tt.r, req.ContentLength, tt.want)
+			t.Errorf("ContentLength(%T) = %d; want %d", tt.r, req.ContentLength, tt.want)
 		}
 	}
 }