Hmm.  We probably can't active detect file locks on pack files on Windows, can we?  It would be nice if we could support a delete, but only if the repository is reasonably believed to be not-in-use right now.

Within EGit you might be able to check GitProjectData and its repositoryCache to see if the repository is open by this workspace.  If it is, then we know we shouldn't try to delete it.