convert: support windows SVN simple auth provider

hgext/convert/transport.py

@@ -47,6 +47,10 b' def _create_auth_baton(pool):'
         svn.client.get_ssl_client_cert_pw_file_provider(pool),
         svn.client.get_ssl_server_trust_file_provider(pool),
         ]
+    # Platform-dependant authentication methods
+    if hasattr(svn.client, 'get_windows_simple_provider'):
+        providers.append(svn.client.get_windows_simple_provider(pool))
+
     return svn.core.svn_auth_open(providers, pool)
 
 class NotBranchError(SubversionException):