msg.go in exp/nacl/srpc does not compile

by **barry.d.silverman**:

<pre>msg.go fails to compile because Bytes.copy function was removed on November 
18th. 

What steps will reproduce the problem?
8g -o _go_.8 client.go msg.go server.go   
msg.go:124: undefined: bytes.Copy

What is your $GOOS? nacl  $GOARCH? 386


Which revision are you using?  (hg identify)
4a3f8104324e+ tip

Please provide any additional information below.</pre>
