Bump version to 0.4.7

* Hack: change builder tests to always use the current unit test image, instead of hardcoding 'docker-ut'

* Hack: move unit tests to a different source image, to work around issues when docker-ut has more than 1 tag.

Fix a couple critical bugs on the test suite

Allow to push/pull on independent registries (by repository or image ID)

testing|stabilization, issue 973: Use docker-golang PPA and lts-raring kernel

following the 'go vet' suggestions for the docker package.

Bugfixes on documentation code

And not a *random* one from its history.

The test runtime object wasn't properly initialized.

- Runtime: fix panic with unix socket

remove + from minor kernel version for kernels built from git

*Remote API: update progressbar every MIN(1%, 512kB)

* Hack: add a script to create the docker-ut image (busybox + socat)

+ Runtime: mount volumes from a host directory with 'docker run -b'

- Runtime: Fix issue when attaching stdin alone

It's a fork of the mkimage-busybox.sh script and it adds socat to the
image. (socat being needed to add udp support, see #33).

This script, like mkimage-busybox.sh, probably only works on
Debian/Ubuntu.