Update from review comments.

* bzrlib/tests/blackbox/test_branch.py:
(TestRemoteBranch): New class ensuring that working trees are not
created remotely.

* bzrlib/transport/sftp.py:
(SFTPTransport.__init__): Make from_transport parameter private.

* bzrlib/transport/remote.py:
(RemoteTransport.__init__): Make from_transport parameter private.
(RemoteHTTPTransport.__init__): Make from_transport parameter private.
(RemoteHTTPTransport.clone): Use _from_transport as a keyword
parameter.

* bzrlib/transport/http/_urllib.py:
(HttpTransport_urllib.__init__): Make from_transport parameter private.

* bzrlib/transport/http/_pycurl.py:
(PyCurlTransport.__init__): Make from_transport parameter private.

* bzrlib/transport/http/__init__.py:
(HttpTransportBase.__init__): Make from_transport parameter private.

* bzrlib/transport/ftp.py:
(FtpTransport.__init__): Make from_transport parameter private.

* bzrlib/transport/__init__.py:
(ConnectedTransport.__init__): Make from_transport parameter private.
(ConnectedTransport.clone, ConnectedTransport._reuse_for): Use
_from_transport as a keyword parameter.

* bzrlib/tests/commands/test_push.py:
(TestPush.test_push): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_pull.py:
(TestPull.test_pull): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_missing.py:
(TestMissing.test_missing): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_merge.py:
(TestMerge.test_merge): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_init_repository.py:
(TestInitRepository.setUp): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_init.py:
(TestInit.setUp): Don't add self.reset_hooks to cleanup, install_hooks
did it.

* bzrlib/tests/commands/test_checkout.py:
(TestCheckout.test_checkout): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/tests/commands/test_cat.py:
(TestCat.test_cat): Don't add self.reset_hooks to cleanup,
install_hooks did it. Skip the test until sftp transport/server problem
is fixed.

* bzrlib/tests/commands/test_branch.py:
(TestBranch.setUp): Don't add self.reset_hooks to cleanup,
install_hooks did it.

* bzrlib/builtins.py:
(_get_bundle_helper): New function. Factored out from merge and pull.
(cmd_pull.run, cmd_merge.run): Use _get_bundle_helper.
(_merge_helper): Add possible_transports as the last parameter.

* bzrlib/tests/transport_util.py: 
Renamed from bzrlib/tests/TransportUtil.py.  Switch from ftp to sftp
transport and server.