* push_decision expects to always get the package primary 'name'
   as apk_name. ASSERT that and fix problem cases.
   (though - this might need to be reverted, and store the non
    primary name in apk_decision instead to accomodate for better
    backtracking optimizations)
 * fix error reporting of virtual package names
 * make 'assign_name' errors soft. the incorrect packages just are
   no longer consider instead of aborting whole calculation.
 * fix backtracking of virtual packages that are not depended
   directly