exp/ssa: make Parameters values, not addresses.

We explicitly spill all parameters to the frame during initial
SSA construction.  (Later passes will remove spills.)
We now properly handle local Allocs escaping via Captures.

Also: allocate BasicBlock.Succs inline.

R=iant, iant
CC=golang-dev
https://codereview.appspot.com/7231050
cmd/go: add helpful error message when vcs is not found.
Fixes issue 4652.

R=bradfitz, minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/7094049

Committer: Brad Fitzpatrick <bradfitz@golang.org>
codereview: show 'not lgtms' in hg p output (with lgtms)

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/7245043
runtime: clear up lr comments

R=cshapiro
CC=golang-dev
https://codereview.appspot.com/7230052
encoding/json: add test for Unmarshal of malformed data

Roll back CL making primitive type unmarshal faster,
because it broke the Unmarshal of malformed data.

Add benchmarks for unmarshal of primitive types.

Update issue 3949.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7228061
go/build: clean up after rollback

R=rsc
CC=golang-dev
https://codereview.appspot.com/7237049