I wrote this because I received the following error trying to establish a tunnel to a MySQL instance on AppFog:
To use `af tunnel', you must first install Caldecott:
gem install caldecott
Note that you'll need a C compiler. If you're on OS X, Xcode
will provide one. If you're on Windows, try DevKit.
This manual step will be removed in the future.
Error: Caldecott is not installed.