* Caching.
* libdebquery
* Add progress indicators and fork after initializing
* XML/XHTML compliance
* Fix signal stuff
* Sort uninstallability reasons to exhibit a cycle, or even draw a graph.
* Add legend to lifetable

Done
====
* ADD MUTEXES !!! TO INSTALLABILITY STORE.
* Fix navigator (prev.)
* Intervalify installability: look at reasons instead of raw installability
* Genericify charts 
* Charts
* Finer-grained persistance
* Navigation and partial view of resulting tables.
* Versions:
  - rename as unit_info
  - add provides
* Coalescing of stable, unstable etc. for checking
* Gzip output (saves 95% on big tables)
* Date navigation to lifetable
