When installing packages, show which repository they come from

If you have more than one remote-repo setting in your `~/.cabal/config`, `cabal install` might silently pick package from other repository than you expect it to, which may lead to compilation failures and confusion.

I personally was bit by it while installing `vector` package - official Hackage has revision with updated bounds of its dependencies, but I had another repository defined in `~/.cabal/config` that also contained `vector`, but with original bounds. As this repo was defined after Hackage in `~/.cabal/config`, it was silently prioritized and installation of `vector` was failing, because the bounds were wrong and I had no idea what was going on.

I would propose to borrow syntax from Gentoo package manager (that faces the same issues) and, while installing packages, display their names as `package::repository`. I guess the repository part could be skipped if there is only one remote-repo in `~/.cabal/config`.