* Now inherits from BServer, and gets its message port from the
launch_daemon.
* It registers an event "initial_volumes_mounted" that allows other
services to be started afterwards.
* This is now used in the boot launch files, and makes the scripting
based previous solution superfluous which has been removed with this
commit, too.
* This implements the last needed feature in order to reproduce the
complete former boot process using the launch_daemon.
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