delivery.NamedTree hashes the manifest digest with each named path's git object;
catalogue.Manifest.NamedPaths gives the union of the paths, only when every artifact
names some. The named: prefix keeps the value apart from a git tree id.
A package or a non-Go bundle may name its build source; a Go program, an archive, an
image and an upstream artifact refuse the word by name, as do a path leaving the
module's directory, the whole directory and a pattern.
jschoubben