[ANN] Bazaar Externals plugin

[Ian Clatworthy]

Óscar Fuentes wrote:

> it doesn't exist branch the external using the URL on .bzrexternals.

As a high priority, can we please change this filename to be 
.bzrmeta/externals?

We've been discussing policies for "in tree metadata" at this week's 
sprint and, IIUIC, the policy we're adopting is to put stuff like this 
in .bzrmeta. I'll confirm that with Martin today and send out official 
confirmation Real Soon Now.

Ian C.