Convert Tuples to List automagically

@johnynek, after the Injection upgrade, I'm getting this error:

```scala
scala> (10, 100L).as[List[Array[Byte]]]
<console>:12: error: diverging implicit expansion for type com.twitter.bijection.Conversion[(Int, Long),List[Array[Byte]]]
starting with method fromBijection in trait LowPriorityConversion
              (10, 100L).as[List[Array[Byte]]
```

Even though there's no bijection available. Note that the Injection is present:

```scala
scala> import Injection.connect
import Injection.connect

scala> connect[(Int,Long),List[Array[Byte]]]
res4: com.twitter.bijection.Injection[(Int, Long),List[Array[Byte]]] = <function1>
```

Any ideas?