* helm-files.el: Remove helm-dired-mode and all sources/command linked to it.
* helm-mode.el (helm-mode): Signal error when using on incompatible Emacs (<24).
* helm-config.el: Update autoloads.
* helm-files.el (helm-dired-action): Use with-helm-after-update-hook for helm-ff-maybe-mark-candidates.
Remove helm-ff-maybe-mark-candidates from helm-after-update-hook.