Recursive Carthage dependencies

I'm not 100% if this is within the scope of this project, but currently, when adding Carthage dependencies you also have to manually add any Carthage dependencies that they may in their turn depend on.

E.g. I might have an iOS application that depends on BioPass. I add github "LinusU/BioPass" ~> 1.1.1 to my Cartfile, and - carthage: BioPass to the dependencies in project.yml.

Now, BioPass in turns depends on PromiseKit, and Carthage will correctly pick this up and install both BioPass and PromiseKit. However, trying to run the built app will crash with: Library not loaded: @rpath/PromiseKit.framework/PromiseKit.

The current fix is to add - carthage: PromiseKit to the list in project.yml, and then all is well. However, I think it would be excellent if this could be done automatically, as Carthage does.

Start by locating XcodeGen's handling of Carthage dependencies and reproduce the BioPass/PromiseKit example described in the issue. Trace how the generated project represents direct Carthage dependencies, then verify that a transitive framework is available at runtime without adding it manually to project.yml.