debugrebuilddirstate: double check that no transaction is open

Since transaction impact dirstate write, we make sure nobody is trying anything
strange with this internal command.

mercurial/debugcommands.py

@@ -3128,6 +3128,9 b' def debugrebuilddirstate(ui, repo, rev, '
     """
     ctx = scmutil.revsingle(repo, rev)
     with repo.wlock():
+        if repo.currenttransaction() is not None:
+            msg = b'rebuild the dirstate outside of a transaction'
+            raise error.ProgrammingError(msg)
         dirstate = repo.dirstate
         changedfiles = None
         # See command doc for what minimal does.