Or-patterns

It would be nice to be able to do something like:

```
alt (thingie) {
    case (foo)
    case (something_much_like_foo) {
        ...
    }
    ...
}
```

or even

```
case (foo | something_much_like_foo) { 
    ...
}
```

(Feel free to close this if it's a dup of an existing issue.  I heard it was on the feature list but don't see it.)
