go.talks/pkg/socket: prevent use on AppEngine
go.talks/pkg/socket: prevent use on AppEngine

This seems to fix my go.talks deployment on AppEngine. For some reason,
the init function of the socket package is run, which checks for /tmp
and exits if it does not exist.

R=adg
CC=dsymonds, golang-dev
https://codereview.appspot.com/7341051

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

webfd/go-zh.talks,d0f/go-zh.talks,d0f/go-zh.talks,d0f/go-zh.talks,bryanxu/go-zh.talks,bryanxu/go-zh.talks,d0f/go-zh.talks,webfd/go-zh.talks,d0f/go-zh.talks,bryanxu/go-zh.talks,webfd/go-zh.talks,bryanxu/go-zh.talks,bryanxu/go-zh.talks,webfd/go-zh.talks,bryanxu/go-zh.talks,webfd/go-zh.talks,webfd/go-zh.talks,d0f/go-zh.talks