revlog: make a predicate clearer with parens

transaction: extract backupentry registration in a dedicated function We are about to use the 'backupentry' mechanism to allow cleaning up transaction-related temporary files (such as 'changelog.i.a'). We start by extracting the entry registration into its own method for easy reuse. At that point, I would like to rename the backup-file related variable to something generic but I'm a bit short of ideas.

transaction: pass the transaction to 'postclose' callback This mirrors the API for 'pending' and 'finalize' callbacks. I do not have immediate usage planned for it, but I'm sure some callback will be happy to access transaction related data.