- Explicitly allow `find` to match `.`, which otherwise would be
excluded as a dotfile.
- Add special handling to drop the leading `./` that results from the
above, and generate the appropriate local paths without needing it.
- Error when trying to perform certain transformations on file·names
and failing, to better aid diagnosis.
- When a file has no destination (because `destinations` has not been
generated yet), use the fake destination `NOTDEF`. (Make will restart
before this destination is used.)