rsync --link-dest, --delete and hard-link count

[grarpamp]

> cp -al, rsync

Various source changes would likely change some metadata in the old
sets. And it doesn't handle those pesky multiple link-dests.

> overhead ... dirvish ... find ... etc

In C, in rsync, would be a more efficient general solution than any
particular bolt on equivalent.

> option

Of course.

> how do suggest it reports from which trees the file is "deleted"?

There is only one source arg, it is saying deref in regards to that.
The point is to report to the user that the source has not simply
changed, but disappeared entirely. The user can figure out where
their copies of it still are in the link-dest[s] if needed.

Perhaps '^*nosrc' is much better than *deref or *deleting.