Description:
------------
When you use is_callable to check if a method is callable on an interface, it returns true which might be because Classes and Interfaces share the same namespace.

Reproduce code:
---------------
interface MyInterface
{
    function callableFunc();
}

if (is_callable(array("MyInterface", "callableFunc"))) {
    print("Is callable!");
    call_user_func(array("MyInterface", "callableFunc"));
} else {
    print("Is NOT callable!");
}

Expected result:
----------------
Is NOT callable!

Actual result:
--------------
Is callable!

Fatal error:  Cannot call abstract method MyInterface::callableFunc() in path/to/file on line ###