Allow cross-type communication

Sending notifications is possible from

    - manifest
    - gencode-local
    - gencode-remote

Sending a notification from an object means writing to the file "notifications" into
its object:

    echo mytest >> "$__object/notifications" # a type reports something

Reading / Reacting on notifications works by accessing the file
referred to be "$__notifications". All notifications are prefixed with
the object name ($__object_name) and are appended into this file.

To find out, whether a file was copied, run:

    grep __file/etc/passwd:copy "$__notifications"
