use fmt.Fprintf instead of fmt.Fprint

fmt.Fprint does not allow format strings
remove dead code in CmdPush
kill the right containers in runtime_test
use wg.Done() isntead of wg.Add(-1)
replace unreachable returns with panics

Not only is this a more common idiom, it'll make finding bugs easier,
and it'll make porting to Go 1.1 easier.

Go 1.1 will not require the final return or panic because it has a
notion of terminating statements.
remove superfluous panic
change option description to reflect the semantics

At least, for me, 'map' means that there are two values and one is "mapped" to
another.

In this case, just one value is provided (container's port), the other value is
automatically obtained (host's port) and the actual mapping can be seen using
``docker port`` command.
Merge remote-tracking branch 'dominikh/minor-code-touchups'
Merge pull request #322 from sa2ajj/port-map-nitpick

change option description to reflect the semantics
Merge branch 'master' of ssh://github.com/dotcloud/docker
Add versioning to docker image format. IMPORTANT: the format versioning is pegged to docker's versioning, so changes to the format MUST trigger an increment in version number.
Print a less confusing error message when lxcbr0 doesn't exist