Pass along sass's stats object

The `stats` object that's returned from the sass compiler contains some interesting info, particularly `includedFiles` which can be used to develop smarter watchers. Related to dlmanning#279, fixed dlmanning#428

index.js

@@ -62,6 +62,9 @@ const filePush = (file, sassObject, callback) => {
     file.stat.atime = file.stat.mtime = file.stat.ctime = new Date();
   }
 
+  // Pass along some potentially useful data.
+  file.sassStats = sassObject.stats;
+
   callback(null, file);
 };