Backports library changes related to SI-6566 from a419799

The idea of backporting this occured while developing the -source flag
for SI-8126 : withouth this the library breaks at refchecks for a
Scala compiler that checks type aliases variance.

This shoudl be BC and promote good hygiene.

src/library/scala/collection/TraversableLike.scala

@@ -77,7 +77,7 @@ trait TraversableLike[+A, +Repr] extends Any
   import Traversable.breaks._
 
   /** The type implementing this traversable */
-  protected type Self = Repr
+  protected[this] type Self = Repr
 
   /** The collection of type $coll underlying this `TraversableLike` object.
    *  By default this is implemented as the `TraversableLike` object itself,

src/library/scala/collection/generic/GenericClassTagCompanion.scala

@@ -19,7 +19,7 @@ import scala.reflect.ClassTag
  *  @author Aleksandar Prokopec
  */
 abstract class GenericClassTagCompanion[+CC[X] <: Traversable[X]] {
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   def newBuilder[A](implicit ord: ClassTag[A]): Builder[A, CC[A]]
 

src/library/scala/collection/generic/GenericCompanion.scala

@@ -24,7 +24,7 @@ import scala.language.higherKinds
  */
 abstract class GenericCompanion[+CC[X] <: GenTraversable[X]] {
   /** The underlying collection type with unknown element type */
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   /** The default builder for `$Coll` objects.
    *  @tparam A      the type of the ${coll}'s elements

src/library/scala/collection/generic/GenericOrderedCompanion.scala

@@ -19,7 +19,7 @@ import scala.language.higherKinds
  *  @since 2.8
  */
 abstract class GenericOrderedCompanion[+CC[X] <: Traversable[X]] {
-  type Coll = CC[_]
+  protected[this] type Coll = CC[_]
 
   def newBuilder[A](implicit ord: Ordering[A]): Builder[A, CC[A]]
 

src/library/scala/collection/immutable/TrieIterator.scala

@@ -46,7 +46,7 @@ private[collection] abstract class TrieIterator[+T](elems: Array[Iterable[T]]) e
     case x: HashSetCollision1[_]    => x.ks.map(x => HashSet(x)).toArray
   }).asInstanceOf[Array[Iterable[T]]]
 
-  private type SplitIterators = ((Iterator[T], Int), Iterator[T])
+  private[this] type SplitIterators = ((Iterator[T], Int), Iterator[T])
 
   private def isTrie(x: AnyRef) = x match {
     case _: HashTrieMap[_,_] | _: HashTrieSet[_] => true

src/library/scala/collection/parallel/ParSeqLike.scala

@@ -45,7 +45,7 @@ extends scala.collection.GenSeqLike[T, Repr]
    with ParIterableLike[T, Repr, Sequential] {
 self =>
 
-  type SuperParIterator = IterableSplitter[T]
+  protected[this] type SuperParIterator = IterableSplitter[T]
 
   /** A more refined version of the iterator found in the `ParallelIterable` trait,
    *  this iterator can be split into arbitrary subsets of iterators.