net/http: don't ignore Request.Write's Flush error
net/http: don't ignore Request.Write's Flush error

Pointed out by nekotaroh in issue 2645

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/5539045

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