Warn on same export

[TrySound]

Would be great to warn if there is same exports in module. This example is not explicit and could be dangerous.

// mod1
export const param = 0;
// mod2
export const param = 1;
// mod3
export * from './mod1';
export * from './mod2';

[eventualbuddha]

To be clear, this is allowed by the spec and has well-defined semantics. However, you're right that if could indicate a bug. Warning sounds reasonable.

[Rich-Harris]

Released as 0.33