BSolver: Add VerifyInstallation()

... and implement it in LibsolvSolver.
pkgman resolve-dependencies: Verify result

* Make sure that the computed dependencies don't themselves depend on
  the specified package.
* Print only the actual dependencies, not the specified package.
BSolverRepository::AddPackage(): Add optional return parameter

... returning the added BSolverPackage object.
pkgman resolve-dependencies: Print package paths

... instead of package name and version. The command should now
work as required by haikuporter.
pkgman resolve-dependencies: Avoid code duplication
pkgman resolve-dependencies: Improve usage text formatting