[BUNDLE] Allow different diff output

[Szilveszter Farkas]

> Well, to start with, we commonly name the bundle *.patch or .diff or
> .txt so that we can read it as part of the email. :)
>
> It does mean there is a higher chance of corruption by email programs,
> but it makes reviews much easier.

sorry, i forgot that one while posting :(

> I think it is better to do:

i agree.

> But more importantly, is there a reason why 'show_diff_trees' is not
> sufficient for you?

you're right, it could be used...

> diff_cmd_helper doesn't seem to provide a whole lot on top of that.
> But I'm not opposed to updating the diff_cmd_helper api.

...i just cannot see the reason why that

output = sys.stdout

line is in diff_cmd_helper, if it isn't used at all (show_diff_trees
gets sys.stdout as an argument). maybe that confused me a bit.

regards,
szilveszter / phanatic