pkg/resolve: minor fixes

and lots of comments
(also added BitArray hashing)
Makefile: detect changes in base/pkg
Test environment stub for PkgResolve
Added R-based generator
pkgresolvetst: update
pkgresolvetst: add pruning tests
pkg/resolve: optimized away gnrg
added metadatagen_simple
pkg/resolve: improved version pruning
pkg/resolve: check if solution is unsat