Improved mmCIF fractional coordinate reading

Replaced:

```
atom->SetVector(atom->GetX() * cell_a, atom->GetY() * cell_b, atom->GetZ() * cell_c);
```

with:

```
atom->SetVector(pCell->FractionalToCartesian(atom->GetVector()));
```

The old logic fails on non-cubic unit cells. Before on left, after on right.

![output](https://cloud.githubusercontent.com/assets/1449833/3989685/fd6c2f54-28bd-11e4-8755-15c5e208b800.png)

The other edits are whitespace - just my vim autoremoving tabs.