T.constructor should be of type T

Given

``` typescript
class Example {
}
```

The current type of `Example.constructor` is `Function`, but I feel that it should be `typeof Example` instead. The use case for this is as follows:

I'd like to reference the current value of an overridden static property on the current class.

In TypeScript v1.5-beta, doing this requires:

``` typescript
class Example {
static someProperty = "Hello, world!";

constructor() {
// Output overloaded value of someProperty, if it is overloaded.
console.log(
(this.constructor).someProperty
);
}
}

class SubExample {
static someProperty = "Overloaded! Hello world!";

someMethod() {
console.log(
(this.constructor).someProperty
);
}
}
```

After this proposal, the above block could be shortened to:

``` typescript
class Example {
static someProperty = "Hello, world!";

constructor() {
// Output overloaded value of someProperty, if it is overloaded.
console.log(
this.constructor.someProperty
);
}
}

class SubExample {
static someProperty = "Overloaded! Hello world!";

someMethod() {
console.log(
this.constructor.someProperty
);
}
}
```

This removes a cast to the current class.

Use the two class examples in the issue as the behavioral starting point, then trace the TypeScript type-checking rules for instance constructors and static members. Done means the proposed this.constructor accesses type-check without the casts shown, while preserving the intended behavior for subclasses.

Written by the indexing model from the issue text.