[MERGE] Implement reference command

[Jelmer Vernooij]

Aaron Bentley wrote:
> This branch adds a reference command for managing tree-reference branch
> locations, and also ensures that reconfiguring a lightweight checkout
> into a normal branch preserves tree-reference branch locations.

> +# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> +
> +from bzrlib import (
> +    branch as _mod_branch,
> +    bzrdir,
> +    )
> +from bzrlib.tests import TestCaseWithTransport
> +
> +class TestReference(TestCaseWithTransport):

^^ Doesn't this need two empty lines ?

Is there a specific reason why you're using '1.9' + Branch8 rather than
'development-subtree' ?

bb:tweak

Cheers,

Jelmer