Code review comment for lp:~rockstar/launchpad/fix-launchpad-dev

This branch fixes bug #403839 - There was a launchpad.dev link being generated
by the javascript.

I could've just fixed the HTML being generated, but I thought I'd rather
experiment with dealing with entire page fragments. The UI is exactly the same
as before (sans the bugfix), but this way, I'm not duplicating HTML.

The way that I do this is subject to change, as I have two more branches to
play around with this idea. I've chatted with a few people about this, and
each fragment implementation has different pros/cons, and I'd like to find the
easiest to follow, and metal macros are not the easiest.

To test, run the windmill tests in lp/code/windmill/test_branch_links.py

 reviewer deryck

Cheers,
Paul