using the cache of packages

[Federico Bruni]

The documentation explains that when you run 'lb clean', all the 
generated files are removed except the cache directory. I can confirm 
that.
However, when I run again the build it seems that a lot of packages are 
downloaded again. Maybe I'm wrong?
Or there's any option to tell lb to use the cache? (I would expect it 
to be the default though).

Thanks
Federico