Fixing "breaking packages"

[Jan Stolarek]

I'll chip in with my cries. Yesterday I spent 6 hours trying to track down a build problem in GHC 
HEAD. Turned out that it was caused by having two versions of binary package, which were 
installed to satisfy dependencies and silently broke my installation. I spent another hour today 
fixing things. I would like cabal to prevent such things from ever happening, the same way that 
Linux rpm/deb managers keep packages on the system in a consistent state.

Janek