Patch #1574738 by nod_: rewrite tableheader.js.
Merge branch 'JStablehead' of github.com:Twinmat/backdrop into Twinmat-JStablehead
Issue #1574738 by quicksketch: Followup to tableheader modification to make work with Admin menu.
Merge branch '1.x' of github.com:backdrop/backdrop into 1.x