shrink-revlog: make it work on windows (
issue1976)
shrink-revlog: avoid cryptic error when used as an extension
When shrink-revlog is used as an extension, it would produce an error when
switching back to stable because the script will try to execute itself.
transaction: initialize self.journal to None after deletion
This avoid a warning when having an empty transaction, where hg would try to
delete the journal twice.