add a comment explaining the rationale for not using default methods

(desugar bug)

Author: retrostreams

src/main/java/java9/util/stream/Node.java

@@ -58,6 +58,9 @@
  * @since 1.8
  */
 interface Node<T> {
+    // desugar bug: use old streamsupport version because desugar (Canary 6)
+    // doesn't treat the default methods correctly (a Java 8 implementation
+    // leads to AbstractMethodError / ClassCastException and what not)
 
     /**
      * Returns a {@link Spliterator} describing the elements contained in this

src/main/java/java9/util/stream/Nodes.java

@@ -50,6 +50,9 @@
  * @since 1.8
  */
 final class Nodes {
+    // desugar bug: use old streamsupport version because desugar (Canary 6)
+    // doesn't treat the default methods correctly (a Java 8 implementation
+    // leads to AbstractMethodError / ClassCastException and what not)
 
     private Nodes() {
         throw new Error("no instances");