Added backup handling of updating existing backup.
Added backup handling of updating existing backup.

So, you used the backup utility to pull everything down, but then a new nightly was released. With this patch, it will not re-download everything, but only download files where the bottom level directory is missing. 

Therefore, works well until you fail downloading a file. In that case, you should just nuke the entire version directory to be on the safe side and re-run.
juliandunn/opscode-omnitruck,rhass/opscode-omnitruck,glennmatthews/opscode-omnitruck,juliandunn/opscode-omnitruck,rhass/opscode-omnitruck,juliandunn/opscode-omnitruck,chef/opscode-omnitruck,chef/opscode-omnitruck,chef/omnitruck,glennmatthews/opscode-omnitruck,chef/omnitruck,glennmatthews/opscode-omnitruck,chef/omnitruck,rhass/opscode-omnitruck,chef/opscode-omnitruck