Modifies "maybeRewrap" to focus more on the maybe.

Existential types are rewrapped under a bunch of conditions
unless the operation performed on the underlying type returns
the same type by reference equality. That depends on a
foundation of predictability which doesn't exist. The upshot is
that existential types were rewrapped with abandon, even when
the type were identical.

This had both performance and correctness implications.
Note where the test case output changes like so:

  -scala.collection.immutable.List[Any]
  +scala.collection.immutable.List[<?>]

That's correctness.

1 files changed, 11 insertions, 3 deletions

diff --git a/test/files/run/t6329_vanilla.scala b/test/files/run/t6329_vanilla.scala
index a31cd5c72e..f2d843896d 100644
--- a/test/files/run/t6329_vanilla.scala
+++ b/test/files/run/t6329_vanilla.scala
@@ -1,4 +1,12 @@
+import scala.reflect.classTag
+
 object Test extends App {
-  println(classManifest[List[_]])
-  println(scala.reflect.classTag[List[_]])
-}
\ No newline at end of file
+  println(classManifest[scala.List[_]])
+  println(classTag[scala.List[_]])
+  println(classManifest[scala.collection.immutable.List[_]])
+  println(classTag[scala.collection.immutable.List[_]])
+  println(classManifest[Predef.Set[_]])
+  println(classTag[Predef.Set[_]])
+  println(classManifest[scala.collection.immutable.Set[_]])
+  println(classTag[scala.collection.immutable.Set[_]])
+}