net/http: clarify Request fields' client-vs-server semantics
net/http: clarify Request fields' client-vs-server semantics

Fixes Issue 7682

LGTM=adg
R=golang-codereviews, adg
CC=dsymonds, golang-codereviews, iant
https://codereview.appspot.com/83800043

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