[RFC] vim-patch:7.4.455

```
Problem:  Completion for :buf does not use 'wildignorecase'. (Akshay H)

Solution: Pass the 'wildignorecase' flag around.
```

https://code.google.com/p/vim/source/detail?r=ebc72764fa1e74758ae1ef9d3f49301f80fc3aa4
This should be `'fileignorecase'` (as in the original patch) because it's referring to the user-facing option.