empty string, so check_prepare() can't expect factory.prepare() to
change the host on Windows.  This repairs Windows failures in

test_fcgi_factory
test_ftp_factory
test_http_factory
test_icp_factory
test_webdav_source_factory
test_monitor_factory_with_emergency_user
test_monitor_factory_without_emergency_user

Unfortunately, it also exposes 2 new Windows failures in

test_http_factory
test_webdav_source_factory