Rendering differences with node-sass 3.3 and 3.4

Consider:

```
@include component (module) {
@include option(big) {
@include part(part) {
color: red;
}
}
}
```

With node-sass 3.3.3 the output (as I would expect) is:

```
.module.\--big .module__part {
color: red; }
```

With node-sass 3.4.1 the output is:

```
.module.\--big__part {
color: red; }
```

Is this a bug or an expected change? If the latter, how would I achieve the output of the first example?

Start by compiling the provided mixin example with node-sass 3.3.3 and 3.4.1, then inspect how the nested module, option, and part mixins construct their selectors. Done means determining whether the changed output is intentional and documenting or restoring a way to produce the earlier selector output.

Written by the indexing model from the issue text.