doc: add go1.3 note about the http Transport closing Request.Body
doc: add go1.3 note about the http Transport closing Request.Body

LGTM=rsc
R=rsc, r
CC=golang-codereviews
https://codereview.appspot.com/87620043

pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme