godoc: ignore directories that begin with '.'
godoc: ignore directories that begin with '.'

Fixes issue 2017.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/4675047

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang