(mh-before-commands-processed-hook): Rename from mh-folder-updated-hook.
* mh-e.el (mh-process-commands): Rename mh-folder-updated-hook to
mh-before-commands-processed-hook, call new mh-after-commands-processed-hook.
(mh-folders-changed): New variable (for mh-after-commands-processed-hook).