[RFC] vim-patch:7.4.456

```
Problem:  'backupcopy' is global, cannot write only some
          files in a different way.

Solution: Make 'backupcopy' global-local. (Christian Brabandt)
```

https://code.google.com/p/vim/source/detail?r=54194bd6ed607aa0cec07d8a27d4794573eabba9
I think `unsigned` is not allowed. Though `unsigned int` also seems undesirable. In this particular case we can even use `uint8_t` to keep the struct as small as possible. refs: [style guide about integer types](http://neovim.org/develop/style-guide.xml#Integer_Types), [Integer types refactoring guidelines](https://github.com/neovim/neovim/wiki/Integer-types-refactoring-guidelines)