Block scope support is broken

[eekboom]

TypeScript 1.7.5 does not support the block scope for y here when emitting code for ES5:

function test() {
    let x = 42;
    {
        let x = 43;
        console.log(x);
    }

    {
        let y = 77;
        console.log(y);
    }
    {
        let y = 88;
        console.log(y);
    }
}

Compilation result:

function test() {
    var x = 42;
    {
        var x_1 = 43;
        console.log(x_1);
    }
    {
        var y = 77;
        console.log(y);
    }
    {
        var y = 88;
        console.log(y);
    }
}

At least one of the y's should also have been renamed.

(In my "real" code instead of "console.log()" there are local functions that use y and are registered as callbacks. The first function incorrectly uses the value from the second block.)

Related to #1690

[RyanCavanaugh]

function test() {
    let f1, f2;
    {
        let y = 77;
        f1 = () => console.log(y);
    }
    {
        let y = 88;
        f2 = () => console.log(y);
    }
    f1(); // Should print 77, actual: 88
    f2(); // Should print 88, does
}