go.talks/present: log websocket close message to console, not popup
go.talks/present: log websocket close message to console, not popup

On platforms that don't support websockets, this makes the whole
experience a lot less obnoxious.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/10484043

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