dist: include js directory in misc/tour in binary distros

R=campoy, dsymonds
CC=golang-dev
https://codereview.appspot.com/8564043
dist: add .exe extension to tour.exe

Fixes issue 5246.

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/8558044
lib9: add newline to exec error message

R=golang-dev, bradfitz, r
CC=golang-dev
https://codereview.appspot.com/8573043
io: document non-guarantees of io.Closer

R=r, golang-dev
CC=golang-dev
https://codereview.appspot.com/8575043
encoding/json: fix handling of anonymous fields
The old code was incorrect and also broken. It passed the tests by accident.
The new algorithm is:
        1) Sort the fields in order of names.
        2) For all fields with the same name, sort in increasing depth.
        3) Choose the single field with shortest depth.
If any of the fields of a given name has a tag, do the above using
tagged fields of that name only.
Fixes issue 5245.

R=iant
CC=golang-dev
https://codereview.appspot.com/8583044