soonest:
 x cran2deb user
 - build all archs of same package in one go
 x strip all bundle support out

sooner
 - deal with growing database: prune things.
 - put build log into another table
 - add table to mark which packages need xvfb-run; only use xvfb-run for those
   (and only do those sequentially).

later:
 - split up dependency structure to support building under different distributions
 - force'ing to a non-existent alias should fail.