Continue to fix cache failing to resolve dependencies with name collision

[CosynPa]

This continues #2286. In this pull request, any repository "owner/project" is cloned in the directory "project/owner/". So if two repositories have the same name but different owners, they will be cloned in different directories without conflicting.

But I don't think it actually fixes #2150. I'm not sure if that can even be fixed. In #2150 they want different libraries with the same name to exist simultaneously. But when you write "import library" in Xcode, how can Xcode know which library you want?

Another maybe relevant issue is #2616. This pull request doesn't fix it either. As I mentioned in that issue, the root cause is the resolver. Although when this pull request is applied, the fatal error in that issue will disappear, carthage will actually check out the two different repositories into the same working directory (Carthage/Checkouts/Result) leaving mixed contents of the two repositories in the working directory, which may not be what we want.

So what does this pull request solve or improve anyway? It can improve fetching time a little. When people switch forks and then switch back, they don't have to redownload all the branches in the old fork again.

[CosynPa]

I fixed trailing whitespace and other warnings.

[CosynPa]

Anyone review this? Without this, carthage can easily get confused when there are dependencies of different forks. With this pull request, in situations like #2616, at least carthage won't quit with error, so the user can check out the right dependency manually. This is a huge improvement.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.