Be kinder to goals in more places

[ice1000]

Right now we produce errors for goals in some contexts:

Maybe we can produce goal warnings instead.

[valis]

In the last two examples, that's impossible because after '\extends' it expects a name and not an arbitrary expression. And what's the point of putting a goal there anyway?

[ice1000]

We can don't support those cases. I agree that it's kinda pointless to put a goal there