wip: a beginning of the new constraint solver
wip: draft of resolve method
A simplest check for resolve method. Fix a lot of typos
wip: Start migration of tests to the new resolver
Slices from the same package version imply sibling slices of the same version
Slices always require exact same versions of siblings
Adjust tests to the latest slices schema
wip PackagesResolver knows how to call the Resolver
Finish chaining. Exclude the choices from dependencies list
Add temp TODO comments

fix these bugs!
toString for UnitVersion

helps debugging
Temp hack for listing slices of packages w/o dependencies.
ConstraintSolver finds some results

- transitiveConstraints now includes constraints from the originating node.
- inexactTransitiveDeps consider the originating node
- _propagateExactTransDeps considers combinations of constraint/dependency not
  originating from the argument node (can be optimized later)
correctly break out of the iteration

`return false` doesn't break the loop in _.each.
Support constraints "none" and null as "no constraint"

Old tests pass!
Don't enqueue the same node twice
A comment
A comment on how we convert the result of units-resolver to the result of package resolver
A simple test for a constraint solver with a cost function
Simplest cost function implementation