[MERGE] Add --protocol option to 'bzr serve'.

[Ian Clatworthy]

Jelmer Vernooij wrote:

> Having the registry live in cmd_serve.protocol_registry is a bit
> unusual I guess, but it seemed like the cleanest way to do this
> without polluting the top-level namespace of bzrlib.builtins.

Hi Jelmer,

I'd really aren't keen on having a registry of this nature defined in
the UI layer. If I was writing a GUI for Bazaar, I wouldn't expect to
have to load the text UI layer (builtins.py) to access it.

bb:resubmit

As a starting suggestion, perhaps it ought to live in bzrlib.transport?

Ian C.