add method Value() Value to InterfaceValue.

use Value() in print to print underlying value
from interface.

before:
	package main
	import "fmt"
	func main() {
		x := []interface{} {1, "hello", 2.5};
		fmt.Println(x[0], x[1], x[2], x);
	}

	1 hello 2.5 [<non-nil interface> <non-nil interface> <non-nil interface>]

after:
	1 hello 2.5 [1 hello 2.5]

R=r
DELTA=44  (22 added, 16 deleted, 6 changed)
OCL=27139
CL=27141

src/lib/reflect/value.go

@@ -34,6 +34,8 @@ type Value interface {
 	Interface()	interface {};
 }
 
+func NewValue(e interface{}) Value;
+
 // commonValue fields and functionality for all values
 
 type commonValue struct {
@@ -744,6 +746,7 @@ func structCreator(typ Type, addr Addr) Value {
 type InterfaceValue interface {
 	Value;
 	Get()	interface {};	// Get the underlying interface{} value.
+	Value() Value;
 }
 
 type interfaceValueStruct struct {
@@ -754,6 +757,14 @@ func (v *interfaceValueStruct) Get() interface{} {
 	return *(*interface{})(v.addr)
 }
 
+func (v *interfaceValueStruct) Value() Value {
+	i := v.Get();
+	if i == nil {
+		return nil;
+	}
+	return NewValue(i);
+}
+
 func interfaceCreator(typ Type, addr Addr) Value {
 	return &interfaceValueStruct{ commonValue{InterfaceKind, typ, addr} }
 }