A+C: Alex A Skinner (individual CLA)

Generated by addca.

R=gobot
CC=golang-dev
https://codereview.appspot.com/12084043
encoding/xml: Do not pass through invalid utf8 bytes

EscapeText now escapes 0xFFFD returned from DecodeRune as 0xFFFD, rather than passing through the original byte.
Fixes issue 5880.

R=golang-dev, r, bradfitz, adg
CC=golang-dev
https://codereview.appspot.com/11975043

Committer: Andrew Gerrand <adg@golang.org>