CONTRIBUTORS: add Carl Shapiro's golang.org address

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/7220046
runtime: avoid defining the same variable in more than one translation unit
For gccgo runtime and Darwin where -fno-common is the default.

R=iant, dave
CC=golang-dev
https://codereview.appspot.com/7094061
cmd/go: add missing tests

These changes to test.bash were intended to be submitted with CL 6941058, but were accidentally excluded from the original CL.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/7232043