Add ability to determine Actor parent

[kquick]

[Originally submitted by https://github.com/Scony to the GoDaddy fork]

Well, thank you for explanations.I think you may consider adding such feature in the future. It may be very beneficial for the users. The present situation may be a bit confusing, because a child actor actually has no link to its parent as long as it doesn't receive any message form it. Also - from the child actor perspective - how do you know that the "Setup" message came from the parent ? Or even any message ? Without knowing your parent's address you don't know. The only solution that comes to my mind is to ensure that the first message always comes from the parent. Then you can store it and use it. But during writing tests one may accidentally forgot about this constraint and cause some harm. Also, this seem to put pressure on the thespian lib client as he is forced to write extra code.

[sakian-old]

Having a self.myParent variable, similar to the self.myAddress would be definitely helpful!