avoid early evaluation in some Stream's methods #6415
Description
scala> lazy val x = \{ println("evaluated"); 1 }
x: Int = <lazy>
scala> 0 #:: x #:: Stream.empty
res0: scala.collection.immutable.Stream[Int] = Stream(0, ?)
scala> res0.isDefinedAt(0)
evaluated
res1: Boolean = true
I think that It is not lazy to call GenTraversableLike#tail in LinearSeqOptimized#lengthCompare.