runtime: benchmark for appending N bytes should not append N² bytes.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7420051
archive/tar: remove execute bit from common.go

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7422055
cmd/dist: support for NetBSD/ARM
1. when executing a unsupported VFP instruction, the NetBSD kernel somehow
doesn't report SIGILL, and instead just spin and spin, we add a alarm(2)
to detect this case (albeit this is a kernel bug).
2. NetBSD/ARM's VFP11 support is not complete, so temporarily disable it.
3. The default gcc shipped with NetBSD-current mis-optimizes our code
at -O2, so lower the optimization level to -O1 on NetBSD/ARM.

R=dave, rsc
CC=golang-dev
https://codereview.appspot.com/7286044
net: add TCP over IPv6 benchmarks

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7433044
net: add unixgram dial test

Also replaces testing.Errof with testing.Fatalf, make use of ICMP mock.

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7308058
net: fix windows build

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7429049
net: disable unixgram test on Plan 9 and Windows

Fixes build on Plan 9 and Windows.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7454049