invert a.list-group-item declaration

I'd like to invert this declaration to turn possible to wrap all twbs in a class.

```css
.my-wrapper {
  @import "bootstrap.less";
}
```

I think this is useful when you have to apply twbs mixed with another css libs.

So, I have to invert the ```a.list-group-item``` declaration because the actual declaration results in:

```css
a.my-wrapper .list-group-item {
  ...
}
```

What you think about it? Looks useful? There is another way to do this and keep using inverted declarations?