* helm-mode.el: Issue #277 reverse order of sources in completing-read's.
(helm-comp-read): New arg reverse-history.
(helm-completing-read-default-1): Use it.
* helm.el (helm-map): Bind helm-mark-all and helm-unmark-all.
* helm-files.el (helm-find-files-map): Remove helm mark commands.
* helm-mode.el (helm-comp-read): Use nreverse.