Merge pull request scala#1761 from adriaanm/ticket-6692-2.9.x

SI-6692 pickle one more flag bit: EXISTENTIAL

Author: adriaanm

src/library/scala/reflect/generic/Flags.scala

@@ -100,7 +100,8 @@ object ModifierFlags extends ModifierFlags
 
   private final val PKL_MASK       = 0x00000FFF
 
-  final val PickledFlags: Long  = 0xFFFFFFFFL
+  // must pickle EXISTENTIAL for SI-6692
+  final val PickledFlags: Long     = 0x8FFFFFFFFL
 
   private def rawPickledCorrespondence = Array(
     (IMPLICIT, IMPLICIT_PKL),

src/library/scala/reflect/generic/UnPickler.scala

@@ -396,10 +396,7 @@ abstract class UnPickler {
             NullaryMethodType(restpe)
         case EXISTENTIALtpe =>
           val restpe = readTypeRef()
-          val tparams = until(end, readSymbolRef)
-          // binary compatibility: in 2.9.x, Symbol doesn't have setFlag
-          tparams foreach (x => x.asInstanceOf[{ def setFlag(mask: Long): this.type }] setFlag EXISTENTIAL)
-          ExistentialType(tparams, restpe)
+          ExistentialType(until(end, readSymbolRef), restpe)
         case ANNOTATEDtpe =>
           var typeRef = readNat()
           val selfsym = if (isSymbolRef(typeRef)) {