runtime: fix goroutine status corruption
runtime.entersyscall() sets g->status = Gsyscall,
then calls runtime.lock() which causes stack split.
runtime.newstack() resets g->status to Grunning.
This will lead to crash during GC (world is not stopped) or GC will scan stack incorrectly.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/10696043
runtime: use gp->sched.sp for stack overflow check

On x86 it is a few words lower on the stack than m->morebuf.sp
so it is a more precise check. Enabling the check requires recording
a valid gp->sched in reflect.call too. This is a good thing in general,
since it will make stack traces during reflect.call work better, and it
may be useful for preemption too.

R=dvyukov
CC=golang-dev
https://codereview.appspot.com/10709043
cmd/go: add -coverpkg

The new -coverpkg flag allows computing coverage in
one set of packages while running the tests of a different set.

Also clean up some of the previous CL's recompileForTest,
using packageList to avoid the clumsy recursion.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/10705043
crypto/x509: Added RFC 5280, section 4.2.2.1 Authority Information Access

R=agl, agl
CC=gobot, golang-dev
https://codereview.appspot.com/10245048

Committer: Adam Langley <agl@golang.org>
flag: add Getter interface; implement for all Value types

Fixes issue 5383.

R=golang-dev, 0xjnml, r, rsc
CC=golang-dev
https://codereview.appspot.com/10472043

Committer: Rob Pike <r@golang.org>
Merge branch 'master' into gitfix
runtime: remove declaration of function that does not exist

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/10730045
Merge branch 'master' into gitfix