transaction: make validator a private attribute This is similar to releasefn. It holds state that doesn't need to be exposed as part of the public interface. Differential Revision: https://phab.mercurial-scm.org/D4627

transaction: make releasefn a private attribute This is a handle on a callable that is called when the journal is closed. The value is specified at __init__ time. It doesn't need to be exposed on the public interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4626

transaction: make file a private attribute This holds a file handle for the journal file. This file handle should not be touched outside the journal class and doesn't belong on the public interface. Differential Revision: https://phab.mercurial-scm.org/D4625

transaction: make journal a private attribute This attribute tracks the name of the journal file. It is an implementation detail of the current transaction and therefore shouldn't be exposed as part of the interface. Let's mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4624

transaction: make undoname a private attribute This attribute tracks the file pattern to use for undo files. It is an implementation detail of the current transaction semantics and doesn't need to be part of the future transaction interface. So mark it as private. Differential Revision: https://phab.mercurial-scm.org/D4623

transaction: make count and usages private attributes I want to formalize the interface for transactions. As part of doing that, let's take the opportunity to make some attributes non-public. "count" and "usages" track how many times the transaction has been opened/nested/closed/released. This is internal state and doesn't need to be part of the public API. Differential Revision: https://phab.mercurial-scm.org/D4622