runtime: remove syscall.NewCallbackCDecl on Windows

It is not possible to use (there is no declaration in package syscall),
and no one seems to care.

Alex Brainman may bring this back properly for Go 1.3.

Fixes issue 6338.

R=golang-dev, r, alex.brainman
CC=golang-dev
https://codereview.appspot.com/14287043
crypto/tls: document ConnectionState fields

Fixes issue 6456.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/14289043
cmd/go: document relative imports

Fixes issue 3524.

R=golang-dev, iant, r
CC=golang-dev
https://codereview.appspot.com/14296043