Remove references to Option and Tuple2 from runtime.Long.

The dce identified that scala.scalajs.runtime.Long brought
a big chunk of the collection library even in a virtually
empty project like helloworld, through usages of Option
and Tuple2. This commit gets rig of these references.

Additionally, this will likely yield more efficient code.
Merge pull request #309 from sjrd/tidy-runtime-long

Remove references to Option and Tuple2 from runtime.Long.