transaction: fix detection of cycles involving installed jobs

transaction: fix detection of cycles involving installed jobs

A transaction can be acyclic, but when it's added to installed jobs,
a cycle may result.

transaction_verify_order_one() attempts to detect these cases, but it
fails because the installed jobs often have the exact generation number
that makes them look as if they were walked already.

Fix it by resetting the generation numbers of all installed jobs before
detecting cycles.

An alternative fix could be to add the generation counter to the
Manager and use it instead of starting always from 1 in
transaction_activate(). But I prefer not having to worry about it
wrapping around.