[RFC] vim-patch:7.4.261

```
Problem:  When updating the window involves a regexp pattern, an
          interactive substitute to replace a "\n" with a line
          break fails. (Ingo Karkat)
Solution: Set reg_line_lbr in vim_regsub() and vim_regsub_multi().
```

https://code.google.com/p/vim/source/detail?r=43c6cd07c8defd8505acbe479c6970764c08e6f9