add a test for %+v in nested structures.

threw in an embedded one for good measure.

R=rsc
CC=golang-dev
https://golang.org/cl/157058

src/pkg/fmt/fmt_test.go

@@ -40,6 +40,20 @@ type A struct {
 	x	[]int;
 }
 
+type I int
+
+func (i I) String() string	{ return Sprintf("<%d>", i) }
+
+type B struct {
+	i	I;
+	j	int;
+}
+
+type C struct {
+	i	int;
+	B;
+}
+
 var b byte
 
 var fmttests = []fmtTest{
@@ -184,6 +198,10 @@ var fmttests = []fmtTest{
 	fmtTest{"%v", A{1, 2, "a", []int{1, 2}}, `{1 2 a [1 2]}`},
 	fmtTest{"%+v", A{1, 2, "a", []int{1, 2}}, `{i:1 j:2 s:a x:[1 2]}`},
 
+	// +v on structs with Stringable items
+	fmtTest{"%+v", B{1, 2}, `{i:<1> j:2}`},
+	fmtTest{"%+v", C{1, B{2, 3}}, `{i:1 B:{i:<2> j:3}}`},
+
 	// go syntax
 	fmtTest{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
 	fmtTest{"%#v", &b, "(*uint8)(PTR)"},