Allow define the same local variable name in different scope.

[dameng324]

In this C# code:

public void Test()
{
    if (true)
    {
        int num = 1;
        Console.WriteLine(num);
    }

    int num = 2;
    Console.WriteLine(num);
}

The compiler will result these errors:

1. Conflicting variable 'num' is defined below in first num defined,
2. A local variable named 'num' cannot be declared in this scope because it would give a different meaning to 'num', which is already used in a parent or current scope to denote something else in second num defined.

But acutally it's not make sense as they has different scope.

The first num scope can never access the second num, and the second num scope can never access the first num as well.

It will be really nice if I can define my local var name more freely.

[HaloFour]

See: #2574