This requires a DB delete/recreate when upgrading. It changes the server
protocol, and app IDs, so clients cannot interoperate with each other
across this change, nor with the server. Flag day for everyone!
Now apps do not share channel IDs, so a lot of usage of app1 will not
cause the wormhole codes for app2 to get longer.
The main wormhole code is str (unicode in py3, bytes in py2). Most
everything else must be passed as bytes in both py2/py3.
Keep the internal "side" string as a str, to make it easier to merge
with other URL pieces.
