Fix for upgrading git packages

[cldwalker]

Branch for the fix with tests. Also fixes upgrading gist packages. Perhaps the fix belongs in uninstall so that install/uninstall can be the same for git/gist packages?

[josh]

I think this is really a bug with looking up packages by name in the current environment. I think you mentioned you had a rip-find-package somwhere? I'd be great if that command would work with git short names, full urls, or local package paths.

Another issue I've hit with upgrading is when it fails because the new package doesn't exist. Instead of using install, we should prefetch with rip-package, uninstall, then import that new package.

[cldwalker]

Updated branch. Ended up making find_package a helper since the uninstall message also needs a package object, something an executable can't give us.

As for upgrading a non-existant, adding a rip-package didn't work since rip-uninstall still aborted. However, removing $-e worked.