New package promises can't install specific version

Some package managers (e.g., pkgin) permit multiple versions of the same package within a single repository.

When the get-package-data method is called, the only input is "File=$(promiser)".

There are two problems here.

1. In the case where a specific revision is preferred, it's impossible to retrieve the correct one package data from the repo
2. The get-package-data expects back a single package, not allowing for multiple versions.

Later, when repo-install is called, the version requested is the version returned by get-package-data, completely disregarding the version provided by the package promise.