go.talks/present: switch back to using two part "go build and exec"
go.talks/present: switch back to using two part "go build and exec"

Looks like there was a good reason to build and execute the binary
in two steps, instead of using "go run". With "go run", killing the
process would just kill the go tool process, not the child process.

Fixes issue 4266.

R=r
CC=golang-dev
http://codereview.appspot.com/6741057

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