ToDo:

* Cache the LWP::UserAgent in Login.pm?

* Fix Bugzilla::Auth::Login::Stack to allow failure part way down the chain
  (currently, it seems that both CGI and BrowserID have to be last in order
  to report login failures correctly.)
  
* JS inclusions noticeably slow page load. Do we want a local copy of 
  browserid.js? Do the browserid folks object to that? How can we get good 
  performance? How can we avoid including it in every logged-in page? Can we 
  do demand loading onclick, and/or load-on-reveal?

* Fix -8px margin-bottom hack in login-small-additional_methods.html.tmpl