Fix navbar rendering when navigation.stack is empty (bug 1088419)

It shouldn't happen, but we have evidence that it does, my guess
is that there is a race condition somewhere causing the navbar to
be rendered before navigation stack is built.
Merge pull request #747 from diox/fix-navbar-render-when-navigation-stack-is-empty

Fix navbar rendering when navigation.stack is empty (bug 1088419)
remove old waffle test (bug 1091139)
Ask for a long max-age on the iframes, cachebust it with the build id (bug 1087399)