This is now controlled at the top level goji package: these packages are
not even compiled in when using App Engine. This is sensible, since
neither package is of any use there.

The result of this was that builds were broken on windows and app
engine.

Fixes #59.

Fixes #52.

Package bind provides a convenient syntax for binding to sockets, as well as a
fair bit of magic to automatically Do The Right Thing in both development and
production.