@import doesn't seem to work with absolute paths

When I use a full path with the import directive like...

```
@import '/apps/editor/sass.scss';
```

it fails with a...

```
file to import not found or unreadable: '/apps/editor/sass.scss'
```

Even though I have registered the file.

```
Sass.readFile('/apps/editor/sass.scss');
"body {color:red;} p {font-size:1.2em;}"
```

As long as I don't use absolute paths everything seems to work fine.
