new-run for remote packages

For a while, it's been possible to `new-install` remote packages to get at their binaries. But, in the case where you don't need the binaries in your `$PATH` and you always want to use the latest released version, that feels clumsy when we've got the `new-run` command. However, `new-run` only works on local packages. I think it should be quite feasible to allow `new-run` to invoke executables from remote packages (i.e., not project-local), doing basically what `new-install` does except, instead of symlinking the binaries, it invokes them.