throughout: fix broken calls to Printf etc.

I have written a tool to verify Printf calls, and although it's not
ready to be reviewed yet it's already uncovered a spate of problems
in the repository.  I'm sending this CL to break the changes into
pieces; as the tool improves it will find more, I'm sure.

R=rsc
CC=golang-dev
https://golang.org/cl/3427043

src/pkg/reflect/all_test.go

@@ -873,7 +873,7 @@ func TestMap(t *testing.T) {
 		// Check that value lookup is correct.
 		vv := mv.Elem(NewValue(k))
 		if vi := vv.(*IntValue).Get(); vi != int64(v) {
-			t.Errorf("Key %q: have value %d, want %d", vi, v)
+			t.Errorf("Key %q: have value %d, want %d", k, vi, v)
 		}
 
 		// Copy into new map.