Mixed initialization

[vihanb]

Mixed initializations currently don't call default initializers meaning something like this results in an uninitialized a field and therefore a segfault:

public class T {
    public let a = "A"
    public let b: String

    public init(b: String) {
        self.b = b
    }
}

func main() {
    let x = T(b: "B")
    print(x.b) // "B"
    print(x.a) // segfault
}