SwiftService.upload should work with directories like swiftclient.shell.st_upload

[Andrew Otto]

There's a lot of logic in swiftclient.shell.st_upload that helps a user walk a directory and upload it to Swift. I'm writing some Python code using the SwiftService class. Unfortunetly, since the logic to handle directory uploads in stuck in a shell function, I will either have to shell out to `swift upload`, or I will have to import swiftclient.shell.st_upload and pass in arguments as if I gave them on the CLI.

The directory upload logic in st_upload should be moved into SwiftService somewhere.

Thanks!