exchange: create transaction for bundle1 unbundling earlier

changegroup.apply() currently creates a transation if there isn't
already one. Having the callers of that method pass in an existing
transaction seems a little cleaner. To do that, we need to make sure
all callers have a transaction. Since the transaction name is used as
a hook argument (HG_TXNNAME), we need to match the name from
changegroup.apply().

mercurial/exchange.py

@@ -1734,7 +1734,8 b' def unbundle(repo, cg, heads, source, ur'
         # push can proceed
         if not isinstance(cg, bundle2.unbundle20):
             # legacy case: bundle1 (changegroup 01)
-            with repo.lock():
+            txnname = "\n".join([source, util.hidepassword(url)])
+            with repo.lock(), repo.transaction(txnname):
                 r = cg.apply(repo, source, url)
         else:
             r = None