largefiles: put whole rollback-ing process into the same "wlock" scope Before this patch, there are three distinct "wlock" scopes in "overriderollback": 1. "localrepository.rollback" via original "rollback" command, 2. "merge.update" for reverting standin files only, and 3. "overriderollback" specific "wlock" scope (to synchronize largefile dirstate) But these should be executed in the same "wlock" scope for consistency.