Backport Certificate Pinning to FF31ESR

Certificate pinning did not make it into Firefox 31ESR, however the patches should be an easy backport. We should take Mozilla's patches for this when we rebase to FF31.

Relevant Mozilla bugs: https://bugzilla.mozilla.org/show_bug.cgi?id=744204 https://bugzilla.mozilla.org/show_bug.cgi?id=772756