Function pointers should implement the various Fn* types

[carllerche]

The following should work:

#![feature(unboxed_closures)]
#![feature(overloaded_calls)]

fn action<F: FnOnce() -> ()>(cb: F) {
    cb();
}

fn foo() {
    println!("In foo");
}

pub fn main() {
    action(foo);
}

[ftxqxd]

#15448 was already filed to let functions implement FnMut, and was fixed, so all that is required now is the unboxed closure trait hierarchy for the other traits to work as well.

[japaric]

This is working now (I think it has been working for a while).

[alexcrichton]

Thanks @japaric!