Regression in support of -- in options
`src cat <revision> -- <filename>` is used in vc.el in emacs to cat that revision but:
```
$ src cat 3280 -- todo.org
src: -- is not registered
$ src version
src: 1.39
python: 3.12.4
RCS: 5.10.1
platform: linux
```
... a regression from https://gitlab.com/esr/src/-/issues/6 from 5 years ago?
issue