Delete recursively by path

[imsodin]

Not very sophisticated but useful when you want to remove packages in one repository (e.g. to update all of them to a new version).
This is not the same type of recursiveness as in fetch: Fetch looks for dependencies, this (delete -recurse) just looks for packages whose importpaths have the given path as prefix. This is definitely a quick-and-dirty approach, to do this cleanly you would probably have to factor out the dependency resolution from fetch and use it for both fetch and delete.