Allow deployment in read only environment

[alistairc]

I've had a problem when deploying a fubu app which is running without write permissions. I'm deploying the exploded bottle files, but it still tries to write to the file system.

I've found that it's the empty package folders that are the problem. Since they don't contain a .version file they're always considered out-of-date. This pull request fixes that

This is my first pull request, so let me know if I've messed it up :)

[jeremydmiller]

Nice, this has been a longstanding problem a few other folks have hit