Allow wrapped values to be used in place of primitives.

Nobody has claimed this yet.

``` ts
class NumberWrapper {
constructor(private value: number) {}
valueOf(): number { return this.value; }
}

var x = new NumberWrapper(1);

// The right-hand side of an arithmetic operation
// must be of type 'any', 'number' or an enum type.
console.log(2 + x);
```

It would be nice if an arithmetic operation could allow using the wrapped number because it's `valueOf()` method returns the expected primitive type.

This can be generalized to: if type `T` is expected, then a value that implements the following interface can be used.

``` ts
interface Wrapped {
valueOf(): T;
}
```

Start by reproducing the arithmetic example in the issue and tracing TypeScript's arithmetic operand type-checking path; the payload names no source file, test, or entry point. Done means wrapped values with a valueOf() method returning the expected primitive type are accepted in the relevant arithmetic operations, with behavior covered by tests.

Written by the indexing model from the issue text.