* rework ExecOutput and ExecInput enums so that EXEC_OUTPUT_NULL loses its
magic meaning and is no longer upgraded to something else if set explicitly.
-* add a way to remove fds from the fdstore by name, and make logind use it
-
* in the long run: permit a system with /etc/machine-id linked to /dev/null, to
make it lose its identity, i.e. be anonymous. For this we'd have to patch
through the whole tree to make all code deal with the case where no machine