Automatic updates for loaddefs-type files

[Glenn Morris]

I've added automatic updating of ldefs-boot.el and other versioned files
that contain generated autoload information (cl-loaddefs, etc). This is
using the same cron job on fencepost as the autotools stuff. So there's
no need to commit such changes any more (though it's fine if you want to
do so, eg as part of the change that necessitates the update).