Fix one warning and backport upstream hooks in our extremely
customized footer.html.tmpl. (Hooks can be used by extensions
and I have had the fun of non-working extensions in Wikimedia
Bugzilla already before, due to missing hooks.)

Change-Id: I944e55e5e5fd4449c634b263f9c43d202fb21fd3
Merge "Fix one warning and backport upstream hooks in our extremely customized footer.html.tmpl. (Hooks can be used by extensions and I have had the fun of non-working extensions in Wikimedia Bugzilla already before, due to missing hooks.)"