bundle2: lock the repo during unbundle test

We forgot the lock the repo. It's not too bad during tests, but the lock also
still carry some transaction logic. (yes we need to get rid of this)

tests/test-bundle2.t

@@ -72,11 +72,13 b' Create an extension to test bundle2 API'
   > def cmdunbundle2(ui, repo):
   >     """process a bundle2 stream from stdin on the current repo"""
   >     try:
+  >         lock = repo.lock()
   >         try:
   >             bundle2.processbundle(repo, sys.stdin)
   >         except KeyError, exc:
   >             raise util.Abort('missing support for %s' % exc)
   >     finally:
+  >         lock.release()
   >         remains = sys.stdin.read()
   >         ui.write('%i unread bytes\n' % len(remains))
   >