spec: result type of a comparison is always untyped bool

For details see the cited issue.

Fixes issue 4793.

R=rsc, r, iant, ken
CC=golang-dev
https://codereview.appspot.com/7524044
spec: typed indices must be of integer type

The same rules apply for make arguments.

R=r, rsc, iant, ken
CC=golang-dev
https://codereview.appspot.com/7656043
sync/atomic: make unaligned 64-bit atomics crash on 386

R=golang-dev, bradfitz, dvyukov
CC=golang-dev
https://codereview.appspot.com/7702043