Implement Implicit Class with Extension Method

This extends support for headOption in 2.11 while allowing the inherent functionality provided by 2.12 to take precedence once 2.12 is released.

slick/src/main/scala/slick/util/ReadAheadIterator.scala

@@ -43,3 +43,11 @@ trait ReadAheadIterator[+T] extends BufferedIterator[T] {
    } else throw new NoSuchElementException("next on empty iterator");
  }
}

object ReadAheadIterator {

  /** Feature implemented in Scala library 2.12 this maintains functionality for 2.11 */
  implicit class headOptionReverseCompatibility[T](readAheadIterator: ReadAheadIterator[T]){
    def headOption : Option[T] = if (readAheadIterator.hasNext) Some(readAheadIterator.head) else None
  }
}