misc/dist: use archive/tar to generate tarballs
misc/dist: use archive/tar to generate tarballs

For people untarring with -p or as root, preserving file permissions.
This way we don't make tars owned by adg/eng or adg/staff or whatever
machine Andrew was on. Instead, we always build tarballs owned by predictable
users.

Except archive/tar doesn't seem to work.

Updates issue 3209.

R=golang-dev, adg
CC=dsymonds, golang-dev
http://codereview.appspot.com/5796064
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go