Port couchdb_env.sh to Windows

[James Henstridge]

To connect to desktopcouch, we run a shell script to activate desktopcouch (if needed) and determine the CouchDB port number and OAuth credentials.

The script depends on dbus, so is not likely to work out of the box on Windows. So we will need some other way to do this (possibly still using an external script).

Ideally we can ship both implementations with Bindwood, and pick which script is needed at runtime.