appc/actool: remove unnecessary execute bits actool build output

Group and other execute bits are inappropriate for the produced .aci and
embedded app manifest files
Merge pull request #213 from vcaputo/urwgor

appc/actool: remove execute bits from build-created aci file mode
stage1: gitignore stage1/cache
Documentation: Add 'gpg' to build pre-requisites

Commit 00294ed ("stage1: gpg verify and cache retrieved coreos image")
added a dependency to 'gpg'. Add that to list of build pre-requisites.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
stage1: add / to stage1/cache gitignore entry
Merge pull request #220 from penberg/docs/build-gpg

Documentation: Add 'gpg' to build pre-requisites
Merge pull request #216 from jzelinskie/ignore-cache

stage1: gitignore stage1/cache
Documentation: Adding version to hello world example

The actool is failing when validating the manifest.json, as version is missing.
stage1: generate a socket unit for socket-activated ports

 * Generate a systemd socket unit for socket-activated ports
 * Add socket-related path generators and cleanup rest
 * Remove unnecessary systemd unit path mkdirs, just trust the
   stage1 rootfs provides them.
Merge pull request #214 from vcaputo/socketactivation

stage1: generate socket unit for socket-activated ports
*: build a limited version of rkt on non-Linux

This introduces build tags to allow the actual rkt binary to be built on
platforms other than Linux. This does not change our current focus of rocket
being targeted at the Linux/amd64 platform, but means that users on e.g.
OS X and other operating systems can at least use `rkt fetch` to
retrieve ACI images and so forth.
rkt: have commands register themselves
build: only build ACE validator if go linux/amd64 is available
stage1/init: mirror host's /etc/localtime symlink target in rootfs

This suppresses the warning when systemd-nspawn tries recreating the host's
/etc/localtime symlink in the container filesystem.
Merge pull request #226 from vcaputo/mirrorlocalzoneinfo

stage1/init: mirror host's /etc/localtime symlink target in rootfs
fix etcd sha256 in README.md

following the instructions I get a different hash:

$ wget -q https://github.com/coreos/etcd/releases/download/v0.5.0-alpha.4/etcd-v0.5.0-alpha.4-linux-amd64.aci
$ gzip -dc etcd-v0.5.0-alpha.4-linux-amd64.aci > etcd-v0.5.0-alpha.4-linux-amd64.tar
$ sha256sum etcd-v0.5.0-alpha.4-linux-amd64.tar
f9215c18b86f406c7cec4c7b45fd8752b5bfd1a492507d647821c2ce593fbf31 etcd-v0.5.0-alpha.4-linux-amd64.tar
Merge pull request #229 from filippog/fix/etcd-sha256

fix etcd sha256 in README.md
pkg/tarheader: support hard links when building tar headers

This introduces an inode "cache" that can be used when populating a tar
header (pkg/tarheader.Populate), so that any inodes already seen can be
linked to instead of inserting an entire copy of the file into the tar.
pkg/tarheader: cast inode up to uint64

Some systems (FreeBSD included) have uint32 as syscall.Stat_t.Ino
build: Fix non-POSIX commands realpath and mktemp

realpath is not POSIX and not available on all systems.
POSIX mktemp requires a mandatory template argument.