Fix detection of already visited nodes in DependencyResolver. See #280. ...

Fixes a stack overflow for package graphs with cycles.

Emit better error messages for unresolvable dependency trees.

Fix dependency resolution. ...

The "if (parent == root) return pidx;" line needed to be inside the "if(!matches" block.

Optimize dependency version resolution when root dependencies fail.

Fix an error in the dependency resolution due to a signed/unsigned comparison. See #285. ...

Also added some diagnostic output to the dependency resolution algorithm.

Avoid exponential run time in the dependency resolution algorithm if possible. ...

When going through all combinations of package versions, all sub trees of the search space are now skipped for a conflicting node, as those are guaranteed to conflict anyway.

Fix path based dependencies to be ignored for version selections.

Fix unit tests of DependencyResolver.

Fix resolution of optional and path based dependencies.

Correct copyright notices.

Fix handling of overriding selections and let printUpgradesOnly fail gracefully.

Fix dependency resolution for outdated invalid dependencies. ...

Now the invalid dependency is simply ignored as long as it isn't actually chosen.

Move DependencyResolver to its own module and reorder Version<->Dependency.