Bug fix: Slashed note heads

Minor fix. `fill` boolean was backwards. Was filling in Whole notes and half notes, and leaving everything shorter unfilled.
**Bug:**
![image](https://f.cloud.github.com/assets/1631625/2466282/904b40d8-afad-11e3-820b-db223ad30132.png)
**Fixed:**
![image](https://f.cloud.github.com/assets/1631625/2466290/a1343c1a-afad-11e3-9568-84bae144e6ca.png)