core/transaction: fix cycle break attempts outside transaction

core/transaction: fix cycle break attempts outside transaction

Patch fixes some incorrect-looking code in transaction.c.
It could fix cases where Debian users with bad package configurations
had systemd go into an infinite loop printing messages about breaking an
ordering cycle, though I have not reproduced that problem myself.

transaction_verify_order_one() considers jobs/units outside current
transaction when checking whether ordering dependencies cause cycles.
It would also incorrectly try to break cycles at these jobs; this
cannot work, as the break action is to remove the job from the
transaction, which is a no-op if the job isn't part of the transaction
to begin with. The unit_matters_to_anchor() test also looks like it
would not work correctly for non-transaction jobs. Add a check to
verify that the unit is part of the transaction before considering a
job a candidate for deletion.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=752259