Julia: `remotecall_fetch` and `CallMsg` don't accept type (constructor) functions

[andyferris]

We had a problem trying to use remotecall_fetch(OurType, worker, args...) because OurType isn't a Function.

I'm wondering if the types at https://github.com/JuliaLang/julia/blob/master/stdlib/Distributed/src/messages.jl#L39 are too restrictive? Could this be Callable, or Any? (Or might this cause any potential problems with remote workers that I'm not aware of?)

[JeffBezanson]

The field type should be Any, I'd say. The first argument to remotecall etc. is already unrestricted, so that looks like an oversight.