- WASI's ``gethostname()`` is a stub that always fails with OSError
``ENOTSUP``
- skip mailcap ``test`` if subprocess is not available
- WASI process_time clock does not work.
This change also adds a minimal unittest of urllib.response.addbase.
More are needed, but not to cover the small change being made here.
Addresses http://bugs.python.org/issue5418