Forwarding to and from typed actors

[ufownl]

Relates #319.

[Inet-Jenkins]

Can one of the admins verify this patch?

[Neverlord]

I think this PR is a start, but it would make sense to grant dynamically-typed actors access to the new delegate functionality as well.

[ufownl]

I have moved delegate into local_actor and added a test for it. Now the dynamically-typed actors can access to the new delegate functionality.

[Neverlord]

@Inet-Jenkins ok to test

[Neverlord]

It still misses an overload for delegate(const actor& dest, ...), though.

[ufownl]

The new solution you offered has been implemented, and the overload for delegate(const actor& dest, ...) also has been added.

[Neverlord]

Amazing work, as always. I cleaned up the code a bit and renamed the detail::delegate_helper to delegated. This is because users need to be able to type this name. Also, delegating to a dynamically typed actor returns void (there's really nothing that could be inferred here).

Thanks for contributing to CAF, you rock!