runtime: add link to design doc for new scheduler

R=golang-dev, remyoudompheng, bradfitz
CC=golang-dev
https://codereview.appspot.com/7419049
cmd/gc: unbreak exporting of composite literals.

Fixes issue 4932.

R=golang-dev, dave, rsc
CC=golang-dev
https://codereview.appspot.com/7437043