changes for more restricted reflect.SetValue

src/cmd/gofmt/rewrite.go

src/pkg/asn1/asn1_test.go

src/pkg/gob/codec_test.go

src/pkg/gob/decode.go

src/pkg/gob/decoder.go

src/pkg/gob/encode.go

src/pkg/gob/encoder_test.go

src/pkg/json/decode.go

src/pkg/json/decode_test.go

src/pkg/netchan/export.go

src/pkg/netchan/import.go

src/pkg/rpc/server.go

src/pkg/testing/quick/quick.go

src/pkg/xml/read_test.go