Specific paths override more general paths

For example, if your filter file includes paths like:

```
a/b
a/b/c/d
```

Then, if it exists, path `a/b/e` winds up getting ignored. It seems like a better behavior would be for it to issue a warning that path `a/b/c/d` is overridden by the more general path `a/b` which would include path `a/b/e`

Reproduce the case with a filter file containing a/b and a/b/c/d, then trace the path-filtering entry point that decides which paths are ignored. Done means the more-specific path is reported as overridden by the general path, with the behavior covered by an appropriate test.

Written by the indexing model from the issue text.