SuperNode needs to be versioned

[modeswitch]

Filer is not suitable for use in production until the SuperNode has a version number so that existing file systems can be upgraded.

[humphd]

What do you suggest we use for the version number? Maybe the version of filer?

[modeswitch]

The version number should only change when the storage representation changes, prompting a file system upgrade (updating on-disk structures, etc). It should be used to determine which version of the code can operate on the stored data. It would also be great to build an abstraction layer here to minimize changes.

[humphd]

Related to #37.

As an aside, this won't affect MakeDrive that much, because it would simply sync the filesystem back from the server on upgrade. It is something to fix for Filer, though.