+ Registry: added the registry API to the docker docs

* runtime: Move the capabilities detection into a runtime method

* docs: Update commandline Commit doc

* hack: development; issue #374: Refactor 'make hack' making Vagrantfile and VM more useful

* Packaging: connect to Ubuntu key server on port 80

* runtime: Use /proc/mounts instead of mount(8)

Specifically, Ubuntu Precise's cgroup-lite script uses mount -n
to mount the cgroup filesystems so they don't appear in mtab, so
detection always fails unless the admin updates mtab with /proc/mounts.

/proc/mounts is valid on just about every Linux machine in existence and
as a bonus is much easier to parse.

I also removed the regex in favor of a more accurate parser that should
also support monolitic cgroup mounts (e.g. mount -t cgroup none /cgroup).

Use the 80 port with keyserver.ubuntu.com so it works with corporate firewalls

* Contrib: updated mkimage-debian

Use default mirror from debootstrap when not explicitly provided, and add better target directory naming

Improve mkimage-debian script to also tag using the release version number of the final image (6.0.7, 7.0, etc.)

This is as discussed on #447.