Operator/Operand overload checking issue

[tinganho]

TypeScript should not give an error on the following case:

let diff = new Date() - new Date();

Because the Date objects has a valueOf method that will convert the Date object to a number value during arithmetic operations. Or any expression that expects a primitive type.

Source:
http://stackoverflow.com/questions/24764137/why-is-it-possible-to-subtract-date-objects-in-javascript-is-there-any-form-of

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/valueOf

[tinganho]

Oops, already discussed in #5337 and #2361