transaction: make report a private attribute
This is a callable used for logging. It isn't used outside the
transaction code. It doesn't need to be part of the public interface.
Let's mark it as private.
Differential Revision: https://phab.mercurial-scm.org/D4631
transaction: make opener a private attribute
The VFS instance is an implementation detail of the transaction
and doesn't belong as part of the public interface. So mark it as
private.
Differential Revision: https://phab.mercurial-scm.org/D4630
transaction: make after a private attribute
This is another callable that is passed in at __init__ time. It
doesn't need to be part of the public interface.
Differential Revision: https://phab.mercurial-scm.org/D4629