bufio: make it a little clearer how the default Scanner splits lines.
Just commentary, no semantic change.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/8329043
doc/go1.1.html: state that the heap is bigger on 64-bit machines
Be deliberately vague, since the precise details should not be depended upon.
Fixes issue 5155.

R=golang-dev, gri, adg
CC=golang-dev
https://codereview.appspot.com/8283044
api: update next.txt.

Update Issue 4871

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/8287044