No support for "callable" decorators

[gvanrossum]

This works fine:

F = TypeVar('F', bound=Callable[..., Any])
def outer(f: F) -> F:
    def inner(*args):
        return f(*args)
    return cast(F, inner)

@outer
def foo(a: int) -> str:
    return str(a)

However adding this does not work (it reuses the outer decorator from above):

def superouter() -> Callable[[F], F]:
    return outer

@superouter()  # E: Argument 1 has incompatible type Callable[[str], int]; expected None
def bar(b: str) -> int:
    return int(b)

[rwbarton]

This is a duplicate of #1551, though the exact errors seem to have changed a little since then.