Comment 5 for bug 615729

In general, I don't think we want to detect duplicate arguments, mostly because of the aliasing system. (For example I have log=log --short -r-10..-1, but it is nice to override that with a new -r option).

We could, I suppose, determine whether the duplication comes from an alias or not, though if someone uses a different scripting method we wouldn't detect that.

Helping people from making mistakes is nice to do if we can do it tastefully.