rebase: clean up rebasestate from active transaction Previously, rebase assumes the following pattern: rebase: with transaction as tr: # top-level ... tr.__close__ writes rebasestate unlink('rebasestate') However it's possible that "rebase" was called inside a transaction: with transaction as tr1: rebase: with transaction as tr2: # not top-level ... tr2.__close__ does not write rebasestate unlink('rebasestate') tr1.__close__ writes rebasestate That leaves a rebasestate on disk incorrectly. This patch adds "removefilegenerator" to notify transaction code that the state file is no longer needed therefore fixes the issue.