[MERGE] Add send format registry, pt 2

[Ian Clatworthy]

Jelmer Vernooij wrote:
> The attached patch addresses Ian's feedback on my "bzr send" format
> registry patch. It moves cmd_send and cmd_bundle_revisions to a
> separate file, and adds the format registry as
> bzrlib.send.format_registry (rather than inside the cmd_send class).

This is closer but still doesn't have the layering I was looking for.
Sorry that I wasn't clear enough first time around about what I wanted. :-(

bb:resubmit

Let me try again. I think cmd_send() and cmd_bundle_revisions() ought to
remain in builtins.py. I think cmd_send._run() should become a public
API - send.send() - and that cmd_send.run() and
cmd_bundle_revisions.run() ought to just call it. In other words, the
core command shells including help and option delcaration remain in
builtins.py while the logic, format_registry, _send_4() and _send_0_9()
go in send.py. Make sense? If not, ping me on IRC and we'll discuss further.

Ian C.