Only check cache for included or excluded files:

For example, here’s a hypothetical configuration for broccoli-compass so that changing other files (like `*.js` or `*.html`) in a tree does not cause a rebuild:

```javascript
var outputTree = compileCompass(inputTree, {
  filterFromCache: {
    include: [
      '**/*.{scss,sass}'    // only base the input tree’s hash on *.scss and *.sass files
    ]
  }
});
```

Note, this does _not_ affect what files make it to the output tree at all, rather it only makes it easier for subclasses to only rebuild when file types they care about change.
Merge pull request #11 from timmfin/only-check-cache-for-included-or-excluded-files

Only check cache for included or excluded files