[darwinbuild] introducing darwinup

[Kevin Van Vechten]

Last night I committed a project called darwinup to the darwinbuild  
project.

The goal of darwinup is to provide a way to safely test roots built  
with darwinbuild on the base system.  Roots that are installed with  
darwinup can be uninstalled, restoring the system to its original state.

darwinup should be considered experimental at this time, so exercise  
caution while testing it, but I'm not aware of any catastrophic  
problems.  darwinup does not currently back up any extended  
attributes (including resource forks) and I suspect the format of the  
database may change yet, so there might be compatibility issues in  
the near future.

That being said, I'd appreciate any feedback from testing, bug  
reports, or fixes.

Thanks,

Kevin