[PLUGIN] bzr_difftools: added non-local branches

[Stephen Ward]

Hi,

I've updated the bzr_difftools plugin with support for both non-local branches 
(tested with HTTP transport only) and for repository branches that lack a 
working tree.

Doing diff on a non-local branch is really slow, so I would recommend pulling 
the branch locally for anything you need to look at frequently.  But it does 
work now.

Diffs on repository branches without working trees are more useful, at least 
as long as the repository is local.

I also fixed the permissions on temp directory contents, so they're read-only 
now.

See the PluginRegistry for branch and download locations.

-- Steve