looks like variable binding here is not yet supported?
https://issues.scala-lang.org/browse/SUGGEST-25

```
[error] storehaus/storehaus-mysql/src/main/scala/com/twitter/storehaus/mysql/ValueMapper.scala:55: illegal variable in pattern alternative
[error]         case IntValue(d) | LongValue(d) | ShortValue(d) => Some(ChannelBuffers.copiedBuffer(d.toString, UTF_8))
```