frog doesn't check types when doing equality test

[DartBot]

This issue was originally filed by mattsh@google.com

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frog gives no error or warning when doing equality comparison: E.g.., this is legal in frog:
if (4 == "hello") {
}

[jmesserly]

Offhand I don't see why that would be a type error. "==" is conceptually an operator on Object that takes an Object as its argument, similar to Object.equals in Java/C#. I don't see anything and in the "equality" section of the lang spec saying there is some type check here, and it works in the VM, so I think this is by design.

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Added Invalid label.