merging managed dependencies should ONLY work when scope == import explicitly

dependencies of type == pom are useful for standardizing a set of dependencies for use in multiple projects that don't share a dependencyManagement section or a common parent POM. Limiting their use to import operations will severely curtail this option, and can cause a lot of problems with existing builds where modules have a type == pom, and are listed in dependencyManagement so they can be referenced elsewhere.

This is related to MNG-3391, so I'll also link them.