fix F.Option.toArray

* old Implementation __ALWAYS THROWS ClassCastException__
* Java is not Scala. can not use [ClassTag](https://github.com/scala/scala/blob/v2.10.2/src/library/scala/collection/GenTraversableOnce.scala#L479). [java.util.Collection#toArray](http://bit.ly/ZGwS1m) return type __SHOULD NOT__ override. can not create generic array in runtime.
* It should preserve the contracts of Collection#toArray. see javadoc http://bit.ly/11vSnzE