go/doc: print only one newline between paragraphs Fixes issue 2595.
go/doc: print only one newline between paragraphs
Fixes issue 2595.

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/5544068

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go